Definition of "grampus"

Some time after this we saw some very large fish, which I afterwards found were called grampusses.

1789, Olaudah Equiano, chapter 3, in The Interesting Narrative, volume I

The Governor will blow like an old grampus, I know he will,—well, we must stop till he gets his wind again.

1848 November – 1850 December, William Makepeace Thackeray, chapter 19, in The History of Pendennis. […], volumes (please specify |volume=I or II), London: Bradbury and Evans, […], published 1849–1850

‘No. I only opened the door a foot and put my head in. The street lamps shine into that room. I could see him. He was all right. Sleeping like a great grampus. Poor, poor chap.’

1963, Margery Allingham, chapter 20, in The China Governess‎

Blowing like a grampus from every orifice, I leaned on a passing wave which dumped me[.]

1980, Ian Chappell, Chappelli has the last laugh, page 39