Definition of "bannerfish" in English

noun

1. A large sailfish of the species Istiophorus platypterus, of the swordfish family, with a broad banner-like dorsal fin

2. Any of several species of butterflyfish in the genus Heniochus (order Chaetodontiformes) that superficially resemble the Moorish idol (Zanclus cornutus, order Acanthuriformes), though not closely related.