Lewis & Short

rictus, ūs, m. (collat, form rictum, i, n., Lucr. 6, 1195; Cic. Verr. 2, 4, 43, § 94; plur. ricta, Lucr. 5, 1064; cf. Non. 221, 18 sq.) [ringor], the aperture of the mouth, the mouth wide open (esp. for laughing; class.; cf. hiatus): rictus parvissimus, Varr. ap. Non. 456, 9; Lucil. Titin. and Pompon. ib.; Lucr. 6, 1195; Cic. l. l.; Quint. 1, 11, 9; Suet. Claud. 30; Flor. 3, 11 fin.; Hor. S. 1, 10, 7; Juv. 10, 230 al.
Plur., Ov. A. A. 3, 283; id. M. 11, 126.
Of animals, gaping, distended jaws, Ov. M. 1, 741; 2, 481; Juv. 10, 272.
Plur., Lucr. 5, 1064; Ov. M. 3, 674; 4, 97; 6, 378; 11, 59; 14, 65 et saep.

    1. 2. Poet., transf., the opening of the eyes, Luc. 6, 757 Cort.; Sen. Herc. Oet. 1168; 1276.