Thought a great number were employed (5)
I believe the answer is:
mused
'thought' is the definition.
(musing is a kind of thinking)
'a great number were employed' is the wordplay.
I cannot quite understand how this works, but
'number' could be 'm' (M is an example) and 'm' is found within the answer.
'employed' could be 'used' ('use' can be a synonym of 'employ') and 'used' is found within the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for mused that I've seen before include "Reflected in silence" , "Was absorbed in thought" , "Closer" , "Contemplated" , "Thought (to oneself)" .)