Trusty

wiktionary

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From Middle English trusty, tristy, tresty, equivalent to trust +‎ -y.

etymonline

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trusty (adj.)

early 13c., "trusting," from trust (n.) + -y (2). Old English expressed this idea by treowful. Meaning "reliable, to be counted on" is from early 14c. The noun meaning "trustworthy person" is from 1570s; specifically as "a prisoner granted special privileges as reward for good conduct" by 1855.