Source : Webster's Revised Unabridged Dictionary (1913)

Breastpin \Breast"pin`\ (br[e^]st"p[i^]n`), n.
   A pin worn on the breast for a fastening, or for ornament; a
   brooch.

Source : WordNet®

breastpin
     n : a decorative pin worn by women [syn: {brooch}, {broach}]