"small clip with flexible prongs for the hair," 1928, from diminutive of bob (n.2) + pin (n.).
Entries linking to bobby pin
bob n.2
"short hair," 1680s; attested 1570s in sense of "a horse's tail cut short," from earlier bobbe "cluster" (as of leaves), mid-14c., a northern word, perhaps of Celtic origin (compare Irish baban "tassel, cluster," Gaelic babag).
The group of bob words in English is of obscure and mostly colloquial origin; some originally were perhaps vaguely imitative, but they have become more or less entangled and merged in form and sense. As a noun, it has been used over the years in various senses connected by the notion of "round, hanging mass," as of weights at the end of a fishing line (1610s), a pendulum (1752) or a plumb-line (1832). The hair sense was revived with a shift in women's styles starting in 1918 (when the cut was regarded as a sign of radicalism), and the modern noun meaning "a bobbed hair style" dates from 1920.
In the latter years of the decade [1920s] bobbed hair became almost universal among girls in their twenties, very common among women in their thirties and forties, and by no means rare among women of sixty .... Women universally adopted the small cloche hat which fitted tightly on the bobbed head, and the manufacturer of milliner's materials joined the hair-net manufacturer, the hair-pin manufacturer, and the cotton goods and woolen goods and corset manufacturers, among the ranks of depressed industries. [Frederick Lewis Allen, "Only Yesterday"]
Related words include bobby pin, bobby sox, bobsled, bobcat.
pin n.
late Old English pinn "peg or bolt of wood or metal used to hold things in place or fasten them together," from Proto-Germanic *penn- "jutting point or peak" (source also of 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" (as in Luke iv.9 in Vulgate) and so applied to "points" of various sorts, from PIE root *pet- "to rush, to fly."
De Vaan and Watkins say Latin pinna is a derivative of penna, literally "feather" (see pen (n.1)); older theories regarded pinna as a separate word from a root meaning "sharp point." The Latin word also was borrowed in Celtic: Irish pinne "a pin, peg, spigot;" Welsh pin "a pin, pen."
The transition from 'feather' to 'pin' (a slender or pointed instrument) appears to have been through 'pen,' a quill, to ' pen,' a style or stylus, hence any slender or pointed instrument [Century Dictionary]
As a part of a lock or latch, c. 1200; as a control for a mechanical device, late 14c. The modern slender wire pin, used as a fastener for clothing or in sewing, is attested by this name by late 14c., perhaps late 13c. Transferred sense of "leg" is recorded from 1520s and holds the older sense. The meaning "wooden stick or club set up to be knocked down in a game" (skittles, bowling, etc.) is by 1570s.
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.