Thousands of millions of monkeys roll in it (8)
I believe the answer is:
trillion
'thousands of millions of' is the definition.
The definition suggests a singular noun which matches the answer.
'monkeys roll in it' is the wordplay.
'roll in it' can be anagrammed to 'TRILLION'.
Though, I am unsure how this is indicated.
Can you help me to learn more?
(Other definitions for trillion that I've seen before include "One million million" , "1,000,000,000,000" , "1 and 18 zeros" , "A great number" , "Very large number" .)