Spongy dessert knight tucks into after sailor (9)
I believe the answer is:
absorbent
'spongy' is the definition.
('absorbent' can be similar in meaning to 'spongy')
'dessert knight tucks into after sailor' is the wordplay.
'dessert' becomes 'sorbet' (sorbet is a kind of dessert**).
'knight' becomes 'n' (chess).
'tucks into' is an insertion indicator.
'after' is a charade indicator (letters next to each other).
'sailor' becomes 'ab' (abbreviation for able seaman).
'sorbet' placed around 'n' is 'sorbent'.
'sorbent' put after 'ab' is 'ABSORBENT'.
(Other definitions for absorbent that I've seen before include "Such material is able to take in water" , "Able to mop up" , "drinking" , "Permeable" , "Bob ran set (anag.)" .)