The first element is probably related to the Sc verb buck, bukk, ‘to pour forth, gush out’ (DSL), perhaps describing the coastal waters at Buckhaven, which is situated at a point where the Fife coastline swings a little further out into the North Sea. A related element occurs also in Buckie Burn DFL q.v. The second element is certainly Sc haven ‘harbour’, and the ‘fishers of Buckhaven’ are mentioned in the earliest known record from 1527 (Fraser, Wemyss ii no. 187).