Old English triewe (West Saxon), treowe (Mercian) "faithful, trustworthy, honest, steady in adhering to promises, friends, etc.," from Proto-Germanic *treuwaz- "having or characterized by good faith" (cognates: Old Frisian triuwi, Dutch getrouw, Old High German gatriuwu, German treu, Old Norse tryggr, Danish tryg, Gothic triggws "faithful, trusty"), from PIE *drew-o-, a suffixed form of the root *deru-/*dreu- "be firm, solid, steadfast" (cognates: Lithuanian drutas "firm," Welsh drud, Old Irish dron "strong," Welsh derw "true," Old Irish derb "sure"), with specialized sense "wood, tree" and derivatives referring to objects made of wood (see tree (n.)).
Sense of "consistent with fact" first recorded c.1200; that of "real, genuine, not counterfeit" is from late 14c.; that of "conformable to a certain standard" (as true north) is from c.1550. Of artifacts, "accurately fitted or shaped" it is recorded from late 15c. True-love (n.) is Old English treowlufu. True-born (adj.) first attested 1590s. True-false (adj.) as a type of test question is recorded from 1923. To come true (of dreams, etc.) is from 1819.
late 13c., verray "true, real, genuine," later "actual, sheer" (late 14c.), from Anglo-French verrai, Old French verai "true, truthful, sincere; right, just, legal," from Vulgar Latin *veracus, from Latin verax (genitive veracis) "truthful," from verus "true" (source also of Italian vero), from PIE root *were-o- "true, trustworthy" (cognates: Old English wær "a compact," Old Dutch, Old High German war, Dutch waar, German wahr "true;" Welsh gwyr, Old Irish fir "true;" Old Church Slavonic vera "faith," Russian viera "faith, belief"). Meaning "greatly, extremely" is first recorded mid-15c. Used as a pure intensive since Middle English.
ИСТИНА. Общеслав. Суф. производное от истъ "истинный, настоящий". См. истый1.
Яндекс.Словари › Этимологический словарь. — 2004
стало быть Истина - твердость, надежность, вера, БЫТИЕ.