Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
dē-rĭgesco, gŭi, 3, v. inch. n. (occurring only in the perf.), to become stiff or rigid; to curdle (a poet. word): formidine sanguis deriguit, Verg. A. 3, 260: deriguere oculi, were fixed, id. ib. 7, 447; so, oculi, Ov. M. 14, 754: hirsutae comae, id. F. 3, 332: manus, Luc. 3, 613: cervix, Ov. M. 5, 233: Niobe malis, id. ib. 6, 303 (al. diriguit).