Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
convīvātor, ōris, m. [convivor], he who gives an entertainment, the master of a feast (rare), * Hor. S. 2, 8, 73; Liv. 35, 49, 6; Sen. Ira, 3, 37, 3.