buffyoudaoicibaDictYouDict[buff 词源字典]
buff: [16] Buff originally meant ‘buffalo’; it was presumably an alteration of the French word buffe ‘buffalo’. That sense had died out by the early 18th century, but since then the word has undergone a bizarre series of semantic changes. First, it came to mean ‘leather’, originally from buffalo hides, but later from ox hides. This was commonly used in the 16th and 17th centuries for making military uniforms, so be in buff came to mean ‘be in the army’.

Then in the 17th century the associations of ‘hide’ and ‘skin’ led to the expression in the buff ‘naked’. The colour of buff leather, a sort of dull yellowish-brown, led to the word’s adoption in the 18th century as a colour term. In the 19th century, soft buff or suede leather was used for the small pads or wheels used by silversmiths, watchmakers, etc for polishing: hence the verb buff ‘polish’.

And finally, in the 1820s New York City volunteer firemen were known as ‘buffs’, from the colour of their uniforms; thus anyone who was a volunteer or enthusiastic for something became known as a buff (as in ‘film buff’). The buff of blind-man’s buff is a different word. It meant ‘blow, punch’, and was borrowed in the 15th century from Old French buffe, source also of English buffet ‘blow’ [13].

The term blind-man’s buff is first recorded around 1600, some what later than its now obsolete synonym hoodman blind.

=> buffalo, buffet[buff etymology, buff origin, 英语词源]
buff (n.)youdaoicibaDictYouDict
1570s, buffe leather "leather made of buffalo hide," from Middle French buffle "buffalo" (15c., via Italian, from Latin bufalus; see buffalo (n.)).

The color term comes from the hue of buffalo hides (later ox hides). Association of "hide" and "skin" led c. 1600 to in the buff. Buff-colored uniforms of New York City volunteer firefighters since 1820s led to meaning "enthusiast" (1903).
The Buffs are men and boys whose love of fires, fire-fighting and firemen is a predominant characteristic. [N.Y. "Sun," Feb. 4, 1903]
buff (adj.)youdaoicibaDictYouDict
"well-built, hunky," 1980s, from buff (v.) "polish, make attractive."
buff (v.)youdaoicibaDictYouDict
"to polish, make attractive," 1885, in reference to the treatment of buff leather or else to the use of buff cloth in polishing metals, from buff (n.). Related: Buffed; buffing.