Extent of land, or a cage re-entered? (7)
I believe the answer is:
acreage
'extent of land' is the definition.
(I've seen this in another clue)
'a cage re-entered?' is the wordplay.
'entered?' is an insertion indicator.
'cage' enclosing 're' is 'creage'.
'a'+'creage'='ACREAGE'
'or' acts as a link.
(Other definitions for acreage that I've seen before include "plot" , "Area measure" , "Number of area measurements" , "good quantity of land" , "Extent of ground" .)