Middle English trouen, trowen, "accept as true or valid, believe in, give credence to, be of a certain opinion" from Old English treowan, truwian "trust in, believe, be confident; persuade, suggest; make true; be faithful (to), confederate with," from treow "faith, belief." This is from Proto-Germanic *treuwaz "having or characterized by good faith" (source also of Old Saxon truon, Old Frisian trouwa, Dutch vertrouwen "trust," Old High German triuwen, German trauen "hope, believe, trust"), "having or characterized by good faith," reconstructed to be from a suffixed form of PIE root *deru- "be firm, solid, steadfast."

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.

mid-15c., "trustful, confiding" (implied in trustingly), present-participle adjective from trust (v.). Related: Trustingness.

also antitrust, "opposed to the political power or influence of organized business interests," 1890, U.S., from anti- "against" + trust (n.) in the "economic monopoly" sense.

"group of experts assembled to give advice on some matter," occasionally used since early 1900s, it became current in 1933, in reference to the intellectuals gathered by the administration of incoming U.S. President Franklin D. Roosevelt as advisers; from brain (n.) + trust (n.).

1550s, "a written challenge, letter of defiance," from French cartel (16c.), from Italian cartello "placard," diminutive of carta "card" (see card (n.1)).

It came to mean "written agreement between states at war" (1690s), for the exchange of prisoners or some other mutual advantage, then "a written agreement between challengers" of any sort (1889). The sense of "a commercial trust, an association of industrialists" is from 1900, via German Kartell, which is from French. The older U.S. term for that is trust (n.). The usual German name for them was Interessengemeinschaft, abbreviated IG.

"absence of trust; doubt or suspicion," 1510s, from dis- + trust (n.). "The etymologically correct form is mistrust, in which both elements are Teutonic" [Klein].

also intrust, c. 1600, from en- (1) "make, put in" + trust (n.). Related: Entrusted; entrusting.

"lack of confidence, suspicion," late 14c., from mis- (1) "bad, wrong" + trust (n.). Related: Mistrustful; mistrustfulness.

"person who is responsible for the property of another," 1640s, from trust (v.) + -ee.