c.1200, "reliance on the veracity, integrity, or other virtues of someone or something; religious faith," from Old Norse traust "help, confidence, protection, support," from Proto-Germanic abstract noun *traustam (cognates: Old Frisian trast, Dutch troost "comfort, consolation," Old High German trost "trust, fidelity," German Trost "comfort, consolation," Gothic trausti "agreement, alliance"), from Proto-Germanic *treuwaz-, source of Old English treowian "to believe, trust," and treowe "faithful, trusty" (see true, adj.).from c.1300 as "reliability, trustworthiness; trustiness, fidelity, faithfulness;" from late 14c. as "confident expectation" and "that on which one relies." From early 15c. in legal sense of "confidence placed in a one who holds or enjoys the use of property entrusted to him by its legal owner;" mid-15c. as "condition of being legally entrusted." Meaning "businesses organized to reduce competition" is recorded from 1877. Trust-buster is recorded from 1903.

c.1200, from Old Norse treysta "to trust, rely on, make strong and safe," from traust (see trust, n.). Related: Trusted; trusting.