Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ŭlŭlātŭs, ūs, m. [ululo, the shrieker], a howling, wailing, shrieking, as a sound of mourning or lamentation, Verg. A. 4, 667; Ov. M. 3, 179; 5, 153; 8, 447; Plin. 8, 40, 61, § 145: lugubris, Curt. 4, 15, 29; 5, 12, 12; Stat. Th. 9, 178 al.
The wild yells or warwhoops of the Gauls, Caes. B. G. 5, 37; 7, 80.
The wild cries and shouts of the Bacchanals, Cat. 63, 24; Ov. M. 3, 528; 3, 706.