—adj. 1. of or pertaining to Siam, its people, or their language.
2. Thai (def. 3).
3. twin; closely connected; similar.
4. Informal.dual; combined; twofold or two-way: a Siamese sprinkler.
—n. 1. a native of Siam.
2. Thai (def. 2).
3. See Siamese cat. 4. (usually l.c.) a standpipe placed outside a building close to ground level, having two or more openings so that fire engines can pump water to the sprinkler system of the building.