The longnose butterflyfish gets its name for fairly obvious reasons, though it could equally be called the yellowsquare butterflyfish, blackspot butterflyfish or pailfin butterflyfish.
There are actually two different kinds of longnose butterflyfish. This one is the common longnose butterflyfish while there is also a big longnose butterflyfish, which is a little larger and has a slightly longer nose. The Hawaiian name for both these fish is lauwiliwili nukunuku ’oi’oi which, according to John Hoover in his book The Ultimate Guide to Hawaiian Reef Fishes, Sea Turtles, Dolphins, Whales, and Seals, is the longest of all Hawaiian fish names. In the Hawaiian name, lauwiliwili means ‘leaf of the wiliwili tree,’ nukunuku means ‘beak,’ and ’oi’oi means ‘best’ or ‘sharp.’