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.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.