synsacrum

[sin-sak-ruh m, -sey-kruh m]
noun, plural syn·sac·ra [sin-sak-ruh, -sey-kruh] /sɪnˈsæk rə, -ˈseɪ krə/. Ornithology.
  1. a dorsal ridge of bone in the pelvic region of birds, formed by the fusion of certain thoracic, lumbar, sacral, and caudal vertebrae.

Origin of synsacrum

First recorded in 1900–05; syn- + sacrum
Related formssyn·sa·cral, adjectivepre·syn·sa·cral, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018