Heavy breather coming round to eat spread (7)
I believe the answer is:
grampus
'heavy breather' is the definition.
(type of dolphin)
'coming round to eat spread' is the wordplay.
'coming round' shows that the letters should be reversed in order.
'to eat' becomes 'sup' (supping is a kind of eating).
'spread' becomes 'marg' (I've seen this before).
'sup'+'marg'='supmarg'
'supmarg' backwards is 'GRAMPUS'.
(Other definitions for grampus that I've seen before include "Killer-whale" , "Good synchronised swimmer" , "Dolphin - killer whale" , "Marine mammal (heavy breather)" , "Popular name for a killer whale" .)