bestyoudaoicibaDictYouDict[best 词源字典]
best: [OE] Best and better, the anomalous superlative and comparative of good, go back to a prehistoric Germanic base *bat-, which is related to the archaic English boot ‘remedy’ (as in to boot) and meant generally ‘advantage, improvement’. Its comparative and superlative were *batizon and *batistaz, which came into Old English as respectively betera and betest (gradually reduced via betst to best). The term best man originated in Scotland; it has gradually replaced the earlier bride(s)man and groomsman.
=> better, boot[best etymology, best origin, 英语词源]
best (adj.)youdaoicibaDictYouDict
Old English beste, reduced by assimilation of -t- from earlier Old English betst "best, first, in the best manner," originally superlative of bot "remedy, reparation," the root word now only surviving in to boot (see boot (n.2)), though its comparative, better, and superlative, best, have been transferred to good (and in some cases well). From Proto-Germanic root *bat-, with comparative *batizon and superlative *batistaz (cognates: Old Frisian, Old Saxon, Middle Dutch best, Old High German bezzist, German best, Old Norse beztr, Gothic batists).
The best-laid schemes o' mice an' men
Gang aft agley,
An' lea'e us nought but grief an' pain,
For promis'd joy!

[Burns]
Best-seller as short for "best-selling book" is from 1902, apparently originally in the publishing trade; best friend was in Chaucer (late 14c.). Best girl is first attested 1881, American English; best man is 1814, originally Scottish, replacing groomsman. To be able to do something with the best of them is recorded by 1748.
best (v.)youdaoicibaDictYouDict
"to get the better of," 1863, from best (adj.). Related: Bested; besting.
best (n.)youdaoicibaDictYouDict
c. 1200, from best (adj.).