'To let blood' definitions:

Definition of 'To let blood'

From: GCIDE

Let \Let\, v. t. [imp. & p. p. Let (Letted (l[e^]t"t[e^]d), [Obs].); p. pr. & vb. n. Letting.] [OE. leten, l[ae]ten (past tense lat, let, p. p. laten, leten, lete), AS. l[=ae]tan (past tense l[=e]t, p. p. l[=ae]ten); akin to OFries. l[=e]ta, OS. l[=a]tan, D. laten, G. lassen, OHG. l[=a]zzan, Icel. l[=a]ta, Sw. l[*a]ta, Dan. lade, Goth. l[=e]tan, and L. lassus weary. The original meaning seems to have been, to let loose, let go, let drop. Cf. Alas, Late, Lassitude, Let to hinder.]
1. To leave; to relinquish; to abandon. [Obs. or Archaic, except when followed by alone or be.] [1913 Webster]
He . . . prayed him his voyage for to let. --Chaucer. [1913 Webster]
Yet neither spins nor cards, ne cares nor frets, But to her mother Nature all her care she lets. --Spenser. [1913 Webster]
Let me alone in choosing of my wife. --Chaucer. [1913 Webster]
2. To consider; to think; to esteem. [Obs.] --Chaucer. [1913 Webster]
3. To cause; to make; -- used with the infinitive in the active form but in the passive sense; as, let make, i. e., cause to be made; let bring, i. e., cause to be brought. [Obs.] [1913 Webster]
This irous, cursed wretch Let this knight's son anon before him fetch. --Chaucer. [1913 Webster]
He . . . thus let do slay hem all three. --Chaucer. [1913 Webster]
Anon he let two coffers make. --Gower. [1913 Webster]
4. To permit; to allow; to suffer; -- either affirmatively, by positive act, or negatively, by neglecting to restrain or prevent. [1913 Webster]
Note: In this sense, when followed by an infinitive, the latter is commonly without the sign to; as to let us walk, i. e., to permit or suffer us to walk. Sometimes there is entire omission of the verb; as, to let [to be or to go] loose. [1913 Webster]
Pharaoh said, I will let you go. --Ex. viii. 28. [1913 Webster]
If your name be Horatio, as I am let to know it is. --Shak. [1913 Webster]
5. To allow to be used or occupied for a compensation; to lease; to rent; to hire out; -- often with out; as, to let a farm; to let a house; to let out horses. [1913 Webster]
6. To give, grant, or assign, as a work, privilege, or contract; -- often with out; as, to let the building of a bridge; to let out the lathing and the plastering. [1913 Webster]
Note: The active form of the infinitive of let, as of many other English verbs, is often used in a passive sense; as, a house to let (i. e., for letting, or to be let). This form of expression conforms to the use of the Anglo-Saxon gerund with to (dative infinitive) which was commonly so employed. See Gerund, 2. " Your elegant house in Harley Street is to let." --Thackeray. In the imperative mood, before the first person plural, let has a hortative force. " Rise up, let us go." --Mark xiv. 42. " Let us seek out some desolate shade." --Shak. [1913 Webster]
To let alone, to leave; to withdraw from; to refrain from interfering with.
To let blood, to cause blood to flow; to bleed.
To let down. (a) To lower. (b) To soften in tempering; as, to let down tools, cutlery, and the like.
To let fly or To let drive, to discharge with violence, as a blow, an arrow, or stone. See under Drive, and Fly.
To let in or To let into. (a) To permit or suffer to enter; to admit. (b) To insert, or imbed, as a piece of wood, in a recess formed in a surface for the purpose.
To let loose, to remove restraint from; to permit to wander at large.
To let off. (a) To discharge; to let fly, as an arrow; to fire the charge of, as a gun. (b) To release, as from an engagement or obligation. [Colloq.]
To let out. (a) To allow to go forth; as, to let out a prisoner. (b) To extend or loosen, as the folds of a garment; to enlarge; to suffer to run out, as a cord. (c) To lease; to give out for performance by contract, as a job. (d) To divulge.
To let slide, to let go; to cease to care for. [Colloq.] " Let the world slide." --Shak. [1913 Webster]

Definition of 'To let blood'

From: GCIDE

Blood \Blood\ (bl[u^]d), n. [OE. blod, blood, AS. bl[=o]d; akin to D. bloed, OHG. bluot, G. blut, Goth. bl[=o][thorn], Icel. bl[=o][eth], Sw. & Dan. blod; prob. fr. the same root as E. blow to bloom. See Blow to bloom.]
1. The fluid which circulates in the principal vascular system of animals, carrying nourishment to all parts of the body, and bringing away waste products to be excreted. See under Arterial. [1913 Webster]
Note: The blood consists of a liquid, the plasma, containing minute particles, the blood corpuscles. In the invertebrate animals it is usually nearly colorless, and contains only one kind of corpuscles; but in all vertebrates, except Amphioxus, it contains some colorless corpuscles, with many more which are red and give the blood its uniformly red color. See Corpuscle, Plasma. [1913 Webster]
2. Relationship by descent from a common ancestor; consanguinity; kinship. [1913 Webster]
To share the blood of Saxon royalty. --Sir W. Scott. [1913 Webster]
A friend of our own blood. --Waller. [1913 Webster]
Half blood (Law), relationship through only one parent.
Whole blood, relationship through both father and mother. In American Law, blood includes both half blood, and whole blood. --Bouvier. --Peters. [1913 Webster]
3. Descent; lineage; especially, honorable birth; the highest royal lineage. [1913 Webster]
Give us a prince of blood, a son of Priam. --Shak. [1913 Webster]
I am a gentleman of blood and breeding. --Shak. [1913 Webster]
4. (Stock Breeding) Descent from parents of recognized breed; excellence or purity of breed. [1913 Webster]
Note: In stock breeding half blood is descent showing one half only of pure breed. Blue blood, full blood, or warm blood, is the same as blood. [1913 Webster]
5. The fleshy nature of man. [1913 Webster]
Nor gives it satisfaction to our blood. --Shak. [1913 Webster]
6. The shedding of blood; the taking of life, murder; manslaughter; destruction. [1913 Webster]
So wills the fierce, avenging sprite, Till blood for blood atones. --Hood. [1913 Webster]
7. A bloodthirsty or murderous disposition. [R.] [1913 Webster]
He was a thing of blood, whose every motion Was timed with dying cries. --Shak. [1913 Webster]
8. Temper of mind; disposition; state of the passions; -- as if the blood were the seat of emotions. [1913 Webster]
When you perceive his blood inclined to mirth. --Shak. [1913 Webster]
Note: Often, in this sense, accompanied with bad, cold, warm, or other qualifying word. Thus, to commit an act in cold blood, is to do it deliberately, and without sudden passion; to do it in bad blood, is to do it in anger. Warm blood denotes a temper inflamed or irritated. To warm or heat the blood is to excite the passions. Qualified by up, excited feeling or passion is signified; as, my blood was up. [1913 Webster]
9. A man of fire or spirit; a fiery spark; a gay, showy man; a rake. [1913 Webster]
Seest thou not . . . how giddily 'a turns about all the hot bloods between fourteen and five and thirty? --Shak. [1913 Webster]
It was the morning costume of a dandy or blood. --Thackeray. [1913 Webster]
10. The juice of anything, especially if red. [1913 Webster]
He washed . . . his clothes in the blood of grapes. --Gen. xiix. 11. [1913 Webster]
Note: Blood is often used as an adjective, and as the first part of self-explaining compound words; as, blood-bespotted, blood-bought, blood-curdling, blood-dyed, blood-red, blood-spilling, blood-stained, blood-warm, blood-won. [1913 Webster]
Blood baptism (Eccl. Hist.), the martyrdom of those who had not been baptized. They were considered as baptized in blood, and this was regarded as a full substitute for literal baptism.
Blood blister, a blister or bleb containing blood or bloody serum, usually caused by an injury.
Blood brother, brother by blood or birth.
Blood clam (Zool.), a bivalve mollusk of the genus Arca and allied genera, esp. Argina pexata of the American coast. So named from the color of its flesh.
Blood corpuscle. See Corpuscle.
Blood crystal (Physiol.), one of the crystals formed by the separation in a crystalline form of the h[ae]moglobin of the red blood corpuscles; h[ae]matocrystallin. All blood does not yield blood crystals.
Blood heat, heat equal to the temperature of human blood, or about 981/2 [deg] Fahr.
Blood horse, a horse whose blood or lineage is derived from the purest and most highly prized origin or stock.
Blood money. See in the Vocabulary.
Blood orange, an orange with dark red pulp.
Blood poisoning (Med.), a morbid state of the blood caused by the introduction of poisonous or infective matters from without, or the absorption or retention of such as are produced in the body itself; tox[ae]mia.
Blood pudding, a pudding made of blood and other materials.
Blood relation, one connected by blood or descent.
Blood spavin. See under Spavin.
Blood vessel. See in the Vocabulary.
Blue blood, the blood of noble or aristocratic families, which, according to a Spanish prover, has in it a tinge of blue; -- hence, a member of an old and aristocratic family.
Flesh and blood. (a) A blood relation, esp. a child. (b) Human nature.
In blood (Hunting), in a state of perfect health and vigor. --Shak.
To let blood. See under Let.
Prince of the blood, the son of a sovereign, or the issue of a royal family. The sons, brothers, and uncles of the sovereign are styled princes of the blood royal; and the daughters, sisters, and aunts are princesses of the blood royal. [1913 Webster]