Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
con-trĕmo, ŭi, 3, v. n., to tremble greatly, to quake (rare): caelum tonitru contremit, Pac. ap. Cic. de Or. 3, 39, 157 (Trag. Rel. v. 413 Rib.): fulminis horribili cum plagā torrida tellus Contremit, Lucr. 5, 1220.