Space available, or filling arena? (7)
I believe the answer is:
storage
'space' is the definition.
'or filling arena?' is the wordplay.
'filling' means one lot of letters goes inside another.
'arena?' becomes 'stage'.
'or' placed inside 'stage' is 'STORAGE'.
'available' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for storage that I've seen before include "Cost of keeping in a warehouse" , "Available space for keeping things" , "Longer-term laying up" , "Charge for use of warehouse" , "What repository provides; so great (anag.)" .)