Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† ulmĭtrĭba, ae, m. [vox hibrida, from ulmus and τρίβω, tero], an elm-rubber, i. e. one that wears out elms, is often beaten with elm-rods, a term of abuse, Plaut. Pers. 2, 4, 7; cf. ulmus.