wellyoudaoicibaDictYouDict[well 词源字典]
well: English has two distinct words well, both of ancient ancestry. The adverb, ‘satisfactorily’ [OE], has relatives throughout the Germanic languages (German wohl, Dutch wel, Swedish väl, and Danish vel), and probably goes back ultimately to the Indo-European base *wel-, *wol-, which also gave English voluntary, wealth, and will.

It was not used as an adjective until the 13th century. Well ‘water-hole’ [OE] is descended from the Germanic base *wal-, *wel- ‘roll’ (source also of English wallet, wallow, waltz, welter, etc), and so etymologically denotes a place where water ‘bubbles’ up. This original notion of turbulent overflowing liquid is better preserved in the related verb well ‘gush’ [OE], which to begin with meant ‘boil’, and hence ‘melt metal’ (‘He made him drink welled lead’, Holy Rood 1300), and produced English weld.

=> voluntary, wealth, will; volume, wallow, waltz, weld, welter[well etymology, well origin, 英语词源]
well (adv.)youdaoicibaDictYouDict
"in a satisfactory manner," Old English wel "abundantly, very, very much; indeed, to be sure; with good reason; nearly, for the most part," from Proto-Germanic *welo- (cognates: Old Saxon wela, Old Norse vel, Old Frisian wel, Dutch wel, Old High German wela, German wohl, Gothic waila "well"), from PIE root *wel- (2) "to wish, will" (cognates: Sanskrit prati varam "at will," Old Church Slavonic vole "well," Welsh gwell "better," Latin velle "to wish, will," Old English willan "to wish;" see will (v.)).

Also used in Old English as an interjection and an expression of surprise. The adjective was in Old English in the sense "in good fortune, happy," from the adverb; sense of "satisfactory" is from late 14c.; "agreeable to wish or desire" is from mid-15c.; "in good health, not ailing" is from 1550s. Well-to-do "prosperous" is recorded from 1825.
well (v.)youdaoicibaDictYouDict
"to spring, rise, gush," Old English wiellan (Anglian wællan), causative of weallan "to boil, bubble up, rise (in reference to a river)" (class VII strong verb; past tense weoll, past participle weallen), from Proto-Germanic *wall- "roll" (cognates: Old Saxon wallan, Old Norse vella, Old Frisian walla, Old High German wallan, German wallen, Gothic wulan "to bubble, boil"), from PIE root *wel- (3) "to turn, roll" (see volvox), on notion of "roiling or bubbling water."
well (n.)youdaoicibaDictYouDict
"hole dug for water, spring of water," Old English wielle (West Saxon), welle (Anglian) "spring of water, fountain," from wiellan (see well (v.)). "As soon as a spring begins to be utilized as a source of water-supply it is more or less thoroughly transformed into a well" [Century Dictionary]. Figurative sense of "source from which anything is drawn" was in Old English.