Hairpin n. : A pin, usually forked, or of bent wire, for fastening the hair in place, -- used by women.

Example:
Can i install a Hairpin trigger on a BT paintball assault rifle?

Taxonomy
Hairpin, free encyclopedia, Hairpin turn, wire, fastener, music, search, hair, commonly used, clevis pins, grooved, shafts, biochemistry, Fred Niblo, nickname, crescendo, decrescendo, disambiguation pages.

Defination from the web:
Hairpin cotter, a formed wire fastener most commonly used in clevis pins. Hairpin clip, a formed wire fastener designed for use in grooved shafts. A stem-loop in biochemistry ... Hairpins, a 1920 film, directed by Fred Niblo. Hairpin, in music, the nickname for crescendo and ...