Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ālĕātōrĭus, a, um, adj. [aleator], pertaining to a gamester: aleatoria damna, in gaming, * Cic. Phil. 2, 27: aleatorium forum calfecimus, gaming-board, August. ap. Suet. Aug. 71: ritu, Gell. 18, 13.
Hence, ālĕātōrĭum, ii, n., the place where games of chance are played, a gaming-house, Sid. Ep. 2, 2.