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Old English triewe (West Saxon), treowe (Mercian) "faithful, trustworthy," from Proto-Germanic *trewwjaz "having or characterized by good faith" (cf. Old Frisian triuwi, Dutch getrouw, Old High German gatriuwu, German treu, Old Norse tryggr, Gothic triggws "faithful, trusty"), perhaps ultimately from PIE *dru- "tree," on the notion of "steadfast as an oak." Cf., from same root, Lithuanian drutas "firm," Welsh drud, Old Irish dron "strong," Welsh derw "true," Old Irish derb "sure."
Sense of "consistent with fact" first recorded c.1200; that of "real, genuine, not counterfeit" is from late 14c.; that of "agreeing with a certain standard" (as true north) is from c.1550. Of artifacts, "accurately fitted or shaped" it is recorded from late 15c.; the verb in this sense is from 1841. True-love (adj.) is recorded from late 15c.; true-born first attested 1590s. True-false as a type of test question is recorded from 1923.