Mas″tiff (?), n.; pl.Mastiffs (�). [Mastives is irregular and unusual.] [Prob. fr. Prov. E. masty, adj., large, n., a great dog, prob. fr. mast fruit, and hence, lit., fattened with mast. There is perh. confusion with OF. mestif mongrel; cf. also F. mâtin mastiff, OF. mastin.] (Zoöl.) A breed of large dogs noted for strength and courage. There are various strains, differing in form and color, and characteristic of different countries.
Mastiff bat(Zoöl.), any bat of the genus Molossus; so called because the face somewhat resembles that of a mastiff.