"of or pertaining to Siam," 1690s; see Siam + -ese. Also from 1690s as a noun meaning "native of Siam." The original Siamese twins (exhibited from 1829) were Chang and Eng (1814-1874), Thai-Chinese natives of Siam who settled in the U.S. Hence Siamesed (adj.) "joined in the manner of Siamese twins" (1830). Siamese cat is attested from 1871.
updated on October 09, 2022