mistrust n.

prefix of Germanic origin affixed to nouns and verbs and meaning "bad, wrong," from Old English mis-, from Proto-Germanic *missa- "divergent, astray" (source also of Old Frisian and Old Saxon mis-, Middle Dutch misse-, Old High German missa-, German miß-, Old Norse mis-, Gothic missa-), perhaps literally "in a changed manner," and with a root sense of "difference, change" (compare Gothic misso "mutually"), and thus possibly from PIE *mit-to-, from root *mei- (1) "to change."

Productive as word-forming element in Old English (as in mislæran "to give bad advice, teach amiss"). In 14c.-16c. in a few verbs its sense began to be felt as "unfavorably," and it came to be used as an intensive prefix with words already expressing negative feeling (as in misdoubt). Practically a separate word in Old and early Middle English (and often written as such). Old English also had an adjective (mislic "diverse, unlike, various") and an adverb (mislice "in various directions, wrongly, astray") derived from it, corresponding to German misslich (adj.). It has become confused with mis- (2).

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

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 (source also of 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," from PIE root *deru- "be firm, solid, steadfast."

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.