Meaning of synsacrum

syn•sac•rum

Pronunciation: (sin-sak'rum, -sā'krum), [key]
— pl. -sac•ra
  1. a dorsal ridge of bone in the pelvic region of birds, formed by the fusion of certain thoracic, lumbar, sacral, and caudal vertebrae.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.