Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
taetro (tētr-) (perf. and sup. perh. not found), āre, 1, v. a. [teter, I.], to render foul, Pac. ap. Non. 178, 7 (Trag. Rel. v. 303 Rib.).