'Law of definite proportions' definitions:

Definition of 'law of definite proportions'

noun

(chemistry) law stating that every pure substance always contains the same elements combined in the same proportions by weight [syn: law of constant proportion, law of definite proportions]

Definition of 'Law of definite proportions'

From: GCIDE

Definite \Def"i*nite\, a. [L. definitis, p. p. of definire: cf. F. d['e]fini. See Define.]
1. Having certain or distinct; determinate in extent or greatness; limited; fixed; as, definite dimensions; a definite measure; a definite period or interval. [1913 Webster]
Elements combine in definite proportions. --Whewell. [1913 Webster]
2. Having certain limits in signification; determinate; certain; precise; fixed; exact; clear; as, a definite word, term, or expression. [1913 Webster]
3. Determined; resolved. [Obs.] --Shak. [1913 Webster]
4. Serving to define or restrict; limiting; determining; as, the definite article. [1913 Webster]
Definite article (Gram.), the article the, which is used to designate a particular person or thing, or a particular class of persons or things; -- also called a definitive. See Definitive, n. -
Definite inflorescence. (Bot.) See {Determinate inflorescence}, under Determinate.
Law of definite proportions (Chem.), the essential law of chemical combination that every definite compound always contains the same elements in the same proportions by weight; and, if two or more elements form more than one compound with each other, the relative proportions of each are fixed. Compare Law of multiple proportions, under Multiple. [1913 Webster]