Rictus

·noun The gape of the mouth, as of birds;

— often resricted to the corners of the mouth.

rictus
rictus, ūs, m. (collat, form rictum, i, n., Lucr. 6, 1195; Cic. Verr. 2, 4, 43, § 94; plur. ricta, L...

A New Latin Dictionary by Charlton T. Lewis Ph.D. and Charles Short, LL. D.
rictus
rictus ūs, m nRIC-, the aperture of the mouth, mouth opened wide : risu diducere rictum Auditoris,...

An Elementary Latin Dictionary