Reportedly greater terrain (4)
I believe the answer is:
moor
'terrain' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'reportedly greater' is the wordplay.
'reportedly' shows a homophone (sound like).
'greater' becomes 'more'.
'more' is a homophone of 'MOOR'.
Can you help me to learn more?
(Other definitions for moor that I've seen before include "Open land - secure a boat - North African" , "Anchor" , "Land mainly high" , "Securely fix" , "Old North African" .)