Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
frĕmĕbundus, a, um, adj. [fremo], making a low roaring, growling, snorting, muttering, murmuring (poet.): tanta moles (Argo), Att. ap. Cic. N. D. 2, 35, 89: illapsu (elephantorum), Sil. 3, 463: tum vero praeceps (Achilles) curru fremebundus ab alto Desilit, Ov. M. 12, 128.