Acanthurus nigricauda was first formally described as a subspecies of Acanthurus gahhm in 1929 by the German zoologists Paul Georg Egmont Duncker and& Erna Mohr with its type locality given as Massau Island in the St Matthias Islands northeast of New Ireland in the Bismarck Archipelago in Papua New Guinea.

The head is usually paler than the body, which is a uniform shade but varies in colour from pale grey to dark brown or nearly black, depending on the fish's mood.

Its range extends from East Africa and Madagascar to the Tuamoto Islands, and from southern Japan to Northern and Eastern Australia and New Caledonia.

The scalpels on the caudal peduncle are retractable and are very sharp; they are displayed when the tail is thrust to the side and are used to slash at rival fish and for protection against predators.

They are deep brown at first, with a yellowish, unnotched caudal fin, and gradually change colour as they reach a length of between 5 and 10 cm (2 and 4 in).