Persecute, but not round Red Square (7)
I believe the answer is:
hundred
'square' is the definition.
The definition and answer can be both quantities as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'persecute but not round red' is the wordplay.
'persecute' becomes 'hound' (hound can mean to harrass or persecute).
'but not' is a deletion indicator.
'round' becomes 'o' (round can mean a round object).
'hound' with 'o' taken out is 'hund'.
'hund'+'red'='HUNDRED'
Can you help me to learn more?
(Other definitions for hundred that I've seen before include "Historical division of a county - number" , "Old part of county" , "Former division of county" , "Century" , "Subdivision of shire; ton" .)