The Collaborative International Dictionary of English v.0.48:

Mongoose \Mon"goose\, Mongoos \Mon"goos\, n.; pl. Mongooses
   1. (Zool.) 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.]
      [1913 Webster]

   2. [Tamil manegos.] A Madagascan lemur (Lemur mongos).
      [Webster 1913 Suppl.]