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n. pl. rictus or ric·tus·es
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.
[Latin, from past participle of ringī, to gape.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.