Origin and history of true-false

late Old English, "intentionally untrue, lying," of religion, "not of the true faith, not in accord with Christian doctrines," from Old French fals, faus "false, fake; incorrect, mistaken; treacherous, deceitful" (12c., Modern French faux), from Latin falsus "deceptive, feigned, deceitful, pretend," also "deceived, erroneous, mistaken," past participle of fallere "deceive, disappoint," which is of uncertain origin (see fail (v.)).

From c. 1200 as "deceitful, disloyal, treacherous; not genuine;" from early 14c. as "contrary to fact or reason, erroneous, wrong." Adopted into other Germanic languages (cognates: German falsch, Dutch valsch, Old Frisian falsk, Danish falsk), though in English alone does the active sense of "deceitful" (a secondary sense in Latin) predominate.

False alarm recorded from 1570s. False step (1700) translates French faux pas. To bear false witness is attested from mid-13c. False prophet "one who prophecies without divine commission or by evil spirits," is attested from late 13c. The sporting contest false start is attested by 1850.

Middle English treu, from Old English triewe (West Saxon), treowe (Mercian) "faithful, trustworthy, honest, steady in adhering to promises, friends, etc."

This is reconstructed to be from Proto-Germanic *treuwaz "having or characterized by good faith" (source also of Old Frisian triuwi, Dutch getrouw, Old High German gatriuwu, German treu, Old Norse tryggr, Danish tryg, Gothic triggws "faithful, trusty"), according to Watkins this is in turn from a suffixed form of the PIE root *deru- "be firm, solid, steadfast." Compare trig, trow, trust (n.).

The sense of "consistent with fact, conformable to the actual state of things, not false or erroneous" is recorded from c. 1200. The meaning "real, genuine, rightly answering to the description, not counterfeit" is from late 14c.

As "conformable to law or justice" (as in true heir) from c. 1400. The meaning "exact, just, conformable to a certain standard or original" (as true north, true to the original) is by 1540s; in biology, "conforming to a type, norm, or standard of structure," from 1570s.

In reference to artifacts, "accurately fitted or shaped," from late 15c. Of aim, etc. "straight to the target, accurate," by 1801, probably from the sense, in reference to things, of "sure, unerring" (c. 1200). As an adverb, early 13c., from the adjective.

True-born (adj.) "of genuine birth, having right by birth to a title" is attested from 1590s; true-bred also is from 1590s. To come true (of dreams, etc.) is from 1819. For true blue see blue (adj.1). True-penny "honest fellow" is attested from 1580s.