Origin: Mastives is
irregular and unusual] [Prob. Fr. Prov. E. Masty, adj, big, 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. Matin mastiff, OF. Mastin.
A breed of big dogs noted for power and courage. There are different strains, differing in form and colour, and quality of various countries.
Mastiff bat, any bat of the genus Molossus; so called because the person somewhat resembles that of a mastiff.
Source: Websters Vocabulary