tenderyoudaoicibaDictYouDict[tender 词源字典]
tender: English has two distinct words tender, both of which go back ultimately to the Indo- European base *ten- ‘stretch’. The adjective, ‘delicate, fragile’ [13], comes via Old French tendre from Latin tener ‘delicate’, a descendant of *ten- and source also of English tendril [16] (etymologically a ‘tender’ shoot). The verb, ‘offer’ [16], comes from another Old French tendre, which went back to Latin tendere ‘stretch, hold out’ (source of English tend, tendency, etc).
=> tenant, tend, tendril[tender etymology, tender origin, 英语词源]
tender (adj.)youdaoicibaDictYouDict
"soft, easily injured," early 13c., from Old French tendre "soft, delicate; young" (11c.), from Latin tenerem (nominative tener) "soft, delicate; of tender age, youthful," from a derivative of PIE root *ten- "stretch" (see tenet), on the notion of "stretched," hence "thin," hence "weak" or "young." Compare Sanskrit tarunah "young, tender," Greek teren "tender, delicate," Armenian t'arm "young, fresh, green."

Meaning "kind, affectionate, loving" first recorded early 14c. Meaning "having the delicacy of youth, immature" is attested in English from early 14c. Related: Tenderly; tenderness. Tender-hearted first recorded 1530s.
tender (v.)youdaoicibaDictYouDict
"to offer formally," 1540s, from Middle French tendre "to offer, hold forth" (11c.), from Latin tendere "to stretch, extend" (see tenet). The retention of the ending of the French infinitive is unusual (see render (v.) for another example). The noun meaning "formal offer for acceptance" is from 1540s; specific sense of "money that may be legally offered as payment" is from 1740; hence legal tender "currency."
tender (n.)youdaoicibaDictYouDict
"person who tends another," late 15c., probably an agent noun formed from Middle English tenden "attend to" (see tend (v.2)); later extended to locomotive engineers (1825) and barmen (1883). The meaning "small boat used to attend larger ones" first recorded 1670s.