Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
1. tŭbŭlus, i, m. dim. [tubus], a small pipe or tube, a water-pipe.
2. Tŭbŭlus, i, m., a Roman cognomen in the gens Hostilia: L. Hostilius Tubulus, a prœtor A. U. C. 611, Lucil. ap. Cic. N. D. 1, 23, 63; Cic. Att. 12, 5, 3; id. Fin. 4, 28, 77; 5, 22, 62.