The Collaborative International Dictionary
Crissa
Crissum \Cris"sum\ (kr?s"s?m),, n.; pl. Crissa (-s?). [NL.; cf. L. crisso to move the haunches.] (Zo["o]l.) That part of a bird, or the feathers, surrounding the cloacal opening; the under tail coverts.
WordNet
crissa
See crissum