Volunteers with monarch's receipts (7)
I believe the answer is:
takings
'receipts' is the definition.
(I've seen this before)
'volunteers with monarch's' is the wordplay.
'volunteers' becomes 'TA' (abbreviation for Territorial Army).
'with' means one lot of letters go next to another.
'monarch's' becomes 'kings' (male monarch).
'ta'+'kings'='TAKINGS'
(Other definitions for takings that I've seen before include "Cash receipts" , "gold received?" , "What's in the till" , "Monetary receipts" , "Income from sales, etc" .)