'Of necessity' definitions:

Definition of 'of necessity'

adverb

In such a manner as could not be otherwise; "it is necessarily so"; "we must needs by objective" [syn: inevitably, necessarily, of necessity, needs]

From: GCIDE

Necessity \Ne*ces"si*ty\, n.; pl. Necessities. [OE. necessite, F. n['e]cessit['e], L. necessitas, fr. necesse. See Necessary.]
1. The quality or state of being necessary, unavoidable, or absolutely requisite; inevitableness; indispensableness. [1913 Webster]
2. The condition of being needy or necessitous; pressing need; indigence; want. [1913 Webster]
Urge the necessity and state of times. --Shak. [1913 Webster]
The extreme poverty and necessity his majesty was in. --Clarendon. [1913 Webster]
3. That which is necessary; a necessary; a requisite; something indispensable; -- often in the plural. [1913 Webster]
These should be hours for necessities, Not for delights. --Shak. [1913 Webster]
What was once to me Mere matter of the fancy, now has grown The vast necessity of heart and life. --Tennyson. [1913 Webster]
4. That which makes an act or an event unavoidable; irresistible force; overruling power; compulsion, physical or moral; fate; fatality. [1913 Webster]
So spake the fiend, and with necessity, The tyrant's plea, excused his devilish deeds. --Milton. [1913 Webster]
5. (Metaph.) The negation of freedom in voluntary action; the subjection of all phenomena, whether material or spiritual, to inevitable causation; necessitarianism. [1913 Webster]
Of necessity, by necessary consequence; by compulsion, or irresistible power; perforce. [1913 Webster]
Syn: See Need. [1913 Webster]