Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
flā̆grī̆trĭba, ae, m. [flagrum + tero], a whip-spoiler, i. e. one who wears out the whip with being flogged, a comic appellative of a slave, Plaut. Ps. 1, 2, 5.