Siamese /saɪ.əˈmiːz/noun 3adjective 2forms 3 noun3 •(historical) An inhabitant of Siam.(Malaysia, specifically) a member of the Malaysian Siamese community, an ethnic group descended from Thais. •A Siamese cat.The third kitten said her name was Juno, and that she was a Siamese. — 1951 •A connection of tubes or hoses shaped like a letter Y. adjective2 •Of or relating to Siam; Thai.(Malaysia) Of or related to Malaysian Siamese, a community of Thai people who live in Malaysia. •Of a connection of tubes or hoses: shaped like the letter Y. formsSiameses · more Siamese · most Siamese