Breathless diver closer to tug (7)
I believe the answer is:
puffing
'breathless' is the definition.
(thesaurus)
'diver closer to tug' is the wordplay.
'diver' becomes 'puffin' (I've seen this before).
'closer to' indicates one should take the final letters (the letter which ends or closes the word).
The final letter of 'tug' is 'g'.
'puffin'+'g'='PUFFING'
(Other definitions for puffing that I've seen before include "Breathing noisily" , "Blowing tobacco smoke out into the air" , "Breathing heavily" , "advertising" , "Obviously unfit" .)