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Etymology

Outside Southeast Asia, the name "betta" is used specifically to describe B. splendens, despite the term scientifically applying to the entire genus, which includes B. splendens and at least 72 other species. Betta splendens is more accurately called by its scientific name or "Siamese fighting fish" to avoid confusion with the other members of the genus.

English-speakers often pronounce betta as "bay-tuh", after the second letter in the Greek alphabet. However, it is believed the name is derived from the Malay word ikan betta, with ikan meaning "fish" and bettah referring to an ancient warrior tribe, which is pronounced "bet-tah". Alternative sources suggests the name Betta splendens is formed from two languages, consisting of Malay for "enduring fish" and the Latin word for shining.

Another vernacular name for Siamese fighting fish is plakat, often applied to the short-finned ornamental strains, which is derived from the Thai word pla kat (Thai: ปลากัด), which literally means "biting fish". This name is used in Thailand for all members of the Betta genus, which share similar aggressive tendencies, rather than for any specific strain of the Siamese fighting fish. Thus, the term "fighting fish" is used to generalise all Betta species besides the Siamese fighting fish.

Siamese fighting fish were originally given the scientific name Macropodus pugnax in 1849—literally "aggressive fish with big feet", likely in reference to their elongated pelvic fins. In 1897 they were identified with the genus Betta and became known as Betta pugnax, referring to their aggressiveness. In 1909, the species was finally renamed Betta splendens upon the discovery that an existing species was already named pugnax.