Lewis & Short

hĭĕto, āre, v. freq. n. and a. [for hiato, from hio; cf. Diom. p. 336 P.], to open the mouth wide, to gape, yawn (ante-class.): ego dum hieto, Plaut. Men. 3, 1, 4; cf. id. Fragm. ap. Diom. p. 336 P.: praei hercle tu, qui mihi oscitans hietansque restas, Caecil. ib.; Cn. Mat. ib.
*Transf., in gen., to open wide, throw open: hietantur fores, Laber. ap. Diom. p. 336 P. (Com. Rel. v. 89 Rib.).