Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† bombus, i, m., = βόμβος, a hollow, deep sound, a booming, humming, buzzing: Ennius sonum pedum bombum pedum dixit, Fortun. Dial. (v. Enn. p. 183 fin. Vahl.); of bees; of a horn; of the clapping of hands: si (apes) intus faciunt bombum, Varr. R. R. 3, 16, 32: cum tuba … mugit, Et reboat raucum regio cita barbara bombum, Lucr. 4, 546: raucisonos efflabant cornua bombos, Cat. 64, 263: torva mimalloneis inplerunt cornua bombis, Pers. 1, 99 Coningt. ad loc.; Mart. Cap. 1, § 67; 2, § 197: organorum, Serv. ad Verg. A. 7, 23: qui plausuum genera condiscerent (bombos et imbrices et testas vocabant), Suet. Ner. 20 Casaub.