Whale to blow endlessly, about to rise? (7)
I believe the answer is:
grampus
'whale' is the definition.
(grampus is a kind of whale)
'to blow endlessly about to rise?' is the wordplay.
'to blow' becomes 'gust' (as in a gust of wind).
'endlessly' means to remove the last letter.
'about' is an insertion indicator.
'to rise?' becomes 'ramp' (to ramp up is to rise or increase).
'gust' with its last letter taken off is 'gus'.
'gus' placed around 'ramp' is 'GRAMPUS'.
(Other definitions for grampus that I've seen before include "Marine mammal (heavy breather)" , "Popular name for a killer whale" , "huge creature" , "One often spouting" , "danger in the main" .)