adolescentyoudaoicibaDictYouDict[adolescent 词源字典]
adolescent: [15] The original notion lying behind both adolescent and adult is of ‘nourishment’. The Latin verb alere meant ‘nourish’ (alimentary and alimony come from it, and it is related to old). A derivative of this, denoting the beginning of an action, was alēscere ‘be nourished’, hence ‘grow’. The addition of the prefix ad- produced adolēscere.

Its present participial stem, adolēscent- ‘growing’, passed into English as the noun adolescent ‘a youth’ (the adjective appears not to have occurred before the end of the 18th century). Its past participle, adultus ‘grown’, was adopted into English as adult in the 16th century.
=> adult, alimentary, alimony, coalesce, coalition, proletarian, prolific[adolescent etymology, adolescent origin, 英语词源]
adolescent (n.)youdaoicibaDictYouDict
mid-15c., "youth, young man," from Middle French adolescent (15c.) or directly from Latin adolescentem (nominative adolescens) "growing, near maturity, youthful," present participle of adolescere "grow up, come to maturity, ripen," from ad- "to" (see ad-) + alescere "be nourished," hence, "increase, grow up," inchoative of alere "to nourish" (see old). Adolesce was a back-formed verb used early 20c. by H.G. Wells, G.B. Shaw, Louis MacNeice, but it seems not to have taken.
adolescent (adj.)youdaoicibaDictYouDict
1785, from Latin adolescentem (nominative adolescens) "growing, near maturity, youthful," present participle of adolescere "grow up, come to maturity, ripen" (see adolescent (n.)).