Source : Webster's Revised Unabridged Dictionary (1913)

Mongoose \Mon"goose\, Mongoos \Mon"goos\, n. (Zo["o]l.)
   A species of ichneumon ({Herpestes griseus}), native of
   India. Applied also to other allied species, as the African
   banded mongoose ({Crossarchus fasciatus}). [Written also
   {mungoose}, {mungoos}, {mungous}.]

Mongoose \Mon"goose\, n.; pl. {Mongooses}. [Tamil manegos.]
   A Madagascan lemur ({Lemur mongos}).

Source : WordNet®

mongoose
     n : agile grizzled Old World viverrine; preys on snakes and
         rodents