late Old English pinn "peg, bolt," from Proto-Germanic *penn- "jutting point or peak" (cf. Old Saxon pin "peg," Old Norse pinni "peg, tack," Middle Dutch pin "pin, peg," Old High German pfinn, German Pinne "pin, tack") from Latin pinna "a feather, plume;" in plural "a wing;" also "fin, scoop of a water wheel;" also "a pinnacle; a promontory, cape; battlement" (e.g. in Luke iv:9 in Vulgate) and so applied to "points" of various sorts, from PIE *pet- (see pen (n.1)).
Latin pinna and penna "a feather, plume," in plural "a wing," are treated as identical in Watkins, etc., but regarded as separate (but confused) Latin words by Tucker and others, who derive pinna from PIE *spei- "sharp point" (cf. spike (n.1)) and see the "feather/wing" sense as secondary.
The modern slender wire pin is first attested by this name late 14c. Transferred sense of "leg" is recorded from 1520s and hold the older sense. Pin-money "annual sum allotted to a woman for personal expenses on dress, etc." is attested from 1620s. Pins and needles "tingling sensation" is from 1810. The sound of a pin dropping as a type of something all but silent is from 1775.
mid-14c., "to affix with a pin," from pin (n.). Figurative use from 1570s. Related: Pinned; pinning. Sense of "to hold someone or something down so he or it cannot escape" is attested from 1740. In U.S., as a reference to the bestowal of a fraternity pin on a female student as an indication of a relationship, it is attested by 1938. Phrase pin down "define" is from 1951.
acronym for personal identification number, 1981, from the first reference used with redundant number.
A thin rod for securing the ends of fractured bones.
A peg for fixing the crown to the root of a tooth.
A leg (1530+)