Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
2. succussus (subc-), ūs, m. [succutio], a shaking, jolting, Pac. ap. Cic. Tusc. 2, 21, 48 (Trag. Rel. 257 Rib.): membra tremulo succussu quatit, App. M. 3, p. 138, 29.
Plur., Tert. Anim. 49 init.