The Collaborative International Dictionary of English v.0.48:

Hairpin \Hair"pin`\ (-p[i^]n`), n.
   A pin, usually forked, or of bent wire, for fastening the
   hair in place, -- used by women.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hairpin
    n 1: a double pronged pin used to hold women's hair in place

Moby Thesaurus II by Grady Ward, 1.0:

75 Moby Thesaurus words for "hairpin":
   aberrancy, aberration, bend, bendy, bias, branching off, chevron,
   chevronwise, chevrony, circuitousness, corner, crankiness,
   crankled, crook, crooked, crookedness, curve, curvy, declination,
   departure, detour, deviance, deviancy, deviation, deviousness,
   digression, discursion, divagation, divarication, divergence,
   diversion, dogleg, double, drift, drifting, errantry, excursion,
   excursus, exorbitation, flexuosity, flexuous, indirection,
   obliquity, pererration, rambling, sheer, shift, shifting,
   shifting course, shifting path, skew, slant, staggered, straying,
   sweep, swerve, swerving, swinging, switchback, tack, turn, turning,
   twist, twisty, variation, veer, wandering, warp, yaw, zag, zig,
   zigzag, zigzaggery, zigzaggy, zigzagways