Keeping up an empty compartment (6)
I believe the answer is:
afloat
'empty compartment' is the definition.
Both the definition and answer are adjectives. Perhaps there's a link between them I don't understand?
'keeping up an' is the wordplay.
I cannot quite see how this works, but
'an' could be 'a' and 'a' is located in the answer.
The remaining letters 'float' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for afloat that I've seen before include "At sea - in circulation" , "With one's head above water" , "On the surface" , "At sea, on the water" , "Bobbing along?" .)