Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
1. pătĭbŭlus, a, um, adj. [pateo], fastened to a patibulum; yoked, gibbeted, Plaut. Fragm. ap. Non. 221, 13; App. M. 4, p. 147 (in both passages al. leg. patibulatum; v. patibulatus).