Ship to absorb large swell (5)
I believe the answer is:
bloat
'swell' is the definition.
(I know that bloat is a type of swell)
'ship to absorb large' is the wordplay.
'ship' becomes 'boat' (I've seen this before).
'to absorb' indicates putting letters inside.
'large' becomes 'L' (eg in clothes sizes).
'boat' placed around 'l' is 'BLOAT'.
(Other definitions for bloat that I've seen before include "Fill up with gas" , "Puff out" , "Thus treat some fish" , "Make swollen" , "Swell with fluid or gas" .)