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n. pl. rictus or ric·tuses
1. A gaping grimace: "his mouth gaping in a kind of rictus of startled alarm" (Richard Adams).
a. The expanse of an open mouth or a bird's beak.
b. The corner of the mouth or the fleshy area where the upper and lower mandibles of a bird meet.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
rictusA facial contortion or grimace of pain.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
rictusthe expanse of the open mouth, or gape, in an animal, or the throat of the calyx in a flower.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005