Si·a·mese / ˌsīəˈmēz/ • n. (pl. same) 1. dated a native of Siam (now Thailand). 2. old-fashioned term for Thai (the language). 3. (also Siamese cat) a cat of a lightly built short-haired breed characterized by slanting blue eyes and typically pale fur with darker points. • adj. dated of or concerning Siam, its people, or language.