trusty (adj.)youdaoicibaDictYouDict[trusty 词源字典]
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.[trusty etymology, trusty origin, 英语词源]