acornyoudaoicibaDictYouDict[acorn 词源字典]
acorn: [OE] Acorn has no etymological connection with oak; its nearest linguistic relative in English is probably acre. The Old English word was æcern, which may well have derived from æcer ‘open land’ (the related Middle High German ackeran referred to beech mast as well as acorns, and Gothic akran developed more widely still, to mean simply ‘fruit’).

There are cognate words in other, non- Germanic, Indo-European languages, such as Russian yagoda ‘berry’ and Welsh aeron ‘fruits’. Left to develop on its own, æcern would have become modern English achern, but the accidental similarity of oak and corn have combined to reroute its pronunciation.
=> acre[acorn etymology, acorn origin, 英语词源]
fruit (n.)youdaoicibaDictYouDict
late 12c., "any vegetable product useful to humans or animals," from Old French fruit "fruit, fruit eaten as dessert; harvest; virtuous action" (12c.), from Latin fructus "an enjoyment, delight, satisfaction; proceeds, produce, fruit, crops," from frug-, stem of frui "to use, enjoy," from suffixed form of PIE *bhrug- "agricultural produce," also "to enjoy" (see brook (v.)). The Latin word also is the source of Spanish fruto, Italian frutto, German Frucht, Swedish frukt-.

Originally in English meaning all products of the soil (vegetables, nuts, grain, acorns); modern narrower sense is from early 13c. Also "income from agricultural produce, revenue or profits from the soil" (mid-14c.), hence, "profit," the classical sense preserved in fruits of (one's) labor. Meaning "offspring, progeny, child" is from mid-13c.; that of "any consequence, outcome, or result" is from late 14c. Meaning "odd person, eccentric" is from 1910; that of "male homosexual" is from 1935, underworld slang. The term also is noted in 1931 as tramp slang for "a girl or woman willing to oblige," probably from the fact of being "easy picking." Fruit salad recorded from 1861; fruit-cocktail from 1900; fruit-bat by 1869.