Weedy loungers sprawling around the quarter deck (9)
I believe the answer is:
groundsel
'deck' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'weedy loungers sprawling around the quarter' is the wordplay.
I cannot quite see how this works, but
'around' could be 'round' (synonyms) and 'round' is present in the answer.
'quarter' could be 'se' and 'se' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for groundsel that I've seen before include "Plant of daisy family" , "feed to the birds" , "Common weed" , "plant, unwanted?" .)