Stockholder secures backing to gather rent (9)
I believe the answer is:
storeroom
'stockholder' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'secures backing to gather rent' is the wordplay.
'secures' becomes 'moors' (mooring is a kind of securing).
'backing' says the letters should be written in reverse.
'to gather' is an insertion indicator.
'rent' becomes 'tore' ('rend' and 'tear' both mean to rip something).
'moors' in reverse letter order is 'sroom'.
'sroom' placed around 'tore' is 'STOREROOM'.
Can you help me to learn more?
(Other definitions for storeroom that I've seen before include "Where shop keeps stock" , "Depository" , "Eg, pantry or cellar" , "Place for keeping goods" , "Place where things are kept" .)