apterium

See Latin aptera, a- +‎ Ancient Greek πτερόν (pterón, “wing”) + -ium.

apterium (plural apteria)

1. (ornithology) An area of bare (featherless) skin on a bird.
   • 1918, American Ornithologists' Union, The Auk‎:

     The two halves of the lower cervical tract are still separated by an apterium 4 mm. wide, as in the young bird, but contour feathers are now present on the chin and upper throat, so that they are united at their upper ends.

• pteryla