Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
congerro (concerro, Fest. p. 356 Lindem.), ōnis, m. [congero; prop. one who contributes to a common feast; cf. Lorenz ad Plaut. Most. v. 919], a jolly companion, a playfellow (ante-class.), Plaut. Pers. 1, 3, 9; id. Most. 3, 3, 27 (931 Ritschl.); 5, 1, 8; cf. Varr. L. L. 7, p. 55 Müll.