studyoudaoicibaDictYouDict[stud 词源字典]
stud: Stud ‘place where horses are bred’ and stud ‘nail’ [OE] are different words. The former (like stable and stall) denotes etymologically a place where animals ‘stand’, in this case for breeding purposes. It comes from a prehistoric Germanic *stōtham, a derivative of the base *sta-, *stō- ‘stand’ (source also of English stand, and of steed [OE], which originally denoted a ‘male horse used for breeding’).

The use of the word for a ‘man who is highly active and proficient sexually’ dates from the end of the 19th century. The ancestry of stud ‘nail’ is not altogether clear, although it appears to be related to German stützen ‘support’. It originally meant ‘post, support’, a sense preserved in the building term stud ‘upright post to which boards are fixed’, and ‘nail’ (presumed to represent the same word) did not emerge until the 15th century.
=> stand, steed[stud etymology, stud origin, 英语词源]
stud (n.1)youdaoicibaDictYouDict
"nailhead, knob," late 13c., from Old English studu "pillar, prop, post," from Proto-Germanic *stud- (cognates: Old Norse stoð "staff, stick," properly "stay," Middle High German stud, Old English stow "place"), from PIE *stu-, variant of root *sta- "to stand" (see stet). Sense expanded by late 14c. to include ornamental devices fixed in and projecting from a surface. From the Old English meaning comes the specific sense "one of the small beams of a building which form a basis for the walls."
stud (n.2)youdaoicibaDictYouDict
"horse used for breeding," Old English stod "herd of horses, place where horses are kept for breeding," from Proto-Germanic *stodo (cognates: Old Norse stoð, Middle Low German stod, Old High German stuot "herd of horses," German Stute "mare"), from PIE root *sta- "to stand," with derivatives meaning "place or thing that is standing" (cognates: Old Church Slavonic stado "herd," Lithuanian stodas "a drove of horses;" see stet). Sense of "male horse kept for breeding" is first recorded 1803; meaning "man who is highly active and proficient sexually" is attested from 1895; that of "any young man" is from 1929. Stud-poker (1864) is said to be from stud-horse poker, but that phrase is not found earlier than 1879.
stud (v.)youdaoicibaDictYouDict
c. 1500, "set with studs;" 1560s in studded with "as though sprinkled with nails with conspicuous heads;" from stud (n.1).