Origin and history of child-proof

Old English cild "fetus, infant, unborn or newly born person," from Proto-Germanic *kiltham (source also of Gothic kilþei "womb," inkilþo "pregnant;" Danish kuld "children of the same marriage;" Old Swedish kulder "litter;" Old English cildhama "womb," lit. "child-home"); it has no certain cognates outside Germanic. "App[arently] originally always used in relation to the mother as the 'fruit of the womb'" [Buck].

Also in late Old English, "a youth of gentle birth" (archaic, usually written childe). In 16c.-17c. especially "girl child." The wider sense "young person before the onset of puberty" developed in late Old English. The phrase with child "pregnant" (late 12c.) retains the original sense. The sense extension from "infant" to "child" also is found in French enfant, Latin infans. The meaning "one's own child; offspring of parents" is from late 12c. (the Old English word was bearn; see bairn). Figurative use from late 14c. Most Indo-European languages use the same word for "a child" and "one's child," though there are exceptions (such as Latin liberi/pueri).

The difficulty with the plural began in Old English, where the nominative plural was at first cild, identical with the singular, then c.975 a plural form cildru (genitive cildra) arose, probably for clarity's sake, only to be re-pluraled late 12c. as children, which is thus a double plural. Middle English plural cildre survives in Lancashire dialect childer and in Childermas.

Child abuse is attested by 1963; child-molester from 1950. Child care is from 1915. Child's play, figurative of something easy, is in Chaucer (late 14c.):

I warne yow wel, it is no childes pley To take a wyf withouten auysement. ["Merchant's Tale"]

c. 1200, preove "evidence and argumentation to establish the fact of (something) beyond reasonable doubt," from Anglo-French prove, preove, Old French proeve, prueve "proof, test, experience" (13c., Modern French preuve), from Late Latin proba "a proof," a back-formation from Latin probare "to prove" (see prove). "The devocalization of v to f ensued upon the loss of final e; cf. the relation of v and f in believe, belief, relieve, relief, behove, behoof, etc." [OED, 2nd ed., 1989].

The meaning "act of proving" is early 14c. The meaning "act of testing or making trial of anything" is from late 14c., from influence of prove. The meaning "standard of strength of distilled liquor" is from 1705, on the notion of "having been tested as to degree of strength." The use in photography is from 1855. The typographical sense of "trial impression to test type" is from c. 1600. The numismatic sense of "coin struck to test a die" is from 1762; now mostly in reference to coins struck from highly polished dies, mainly for collectors.

The expression the proof is in the pudding (1915) is a curious perversion of earlier proof of the pudding shall be in the eating (1708), with proof in the sense "quality of proving good or turning out well" (17c.).

word-forming element from proof (adj.) "impenetrable, able to resist" (as in proof against), which is recorded from 1590s, extended from proof (n.) in expressions such as proof of (mid-15c.).

Hence the extended senses involving "of tested power against" in compounds such as storm-proof (1590s), fireproof (1630s), rust-proof (1690s), bomb-proof (1702), waterproof (1725), fool-proof (1902), Milton's branching elm star-proof. A Donne sermon from 1631 has temptation-proof.

In later use often in advertisers' coinages, such as spill-proof, attested from 1909 in reference to carpet sweepers, by 1920 also in newspaper ads for garbage cans, clothes for boys, a dairy pail a cow can't kick over, etc. (It was used by 1902 of a wagon that won't upset.) Kiss-proof is touted as a quality of lipsticks by 1924, earliest of face-powder (1906); in 1890s it was an occasional whimsical word (as in kiss-proof mask, a gift for one suddenly popular). Also child-proof (1933). Shakespeare has shame-proof.