Thought a great many were employed (5)
I believe the answer is:
mused
'thought' is the definition.
(musing is a kind of thinking)
'a great many were employed' is the wordplay.
I cannot really understand how this works, but
'many' could be 'm' (Roman numeral for a thousand) and 'm' is located in the answer.
'employed' could be 'used' ('use' can be a synonym of 'employ') and 'used' is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for mused that I've seen before include "Thought (to oneself)" , "Was absorbed in thought" , "Was deep in thought" , "Reflected or pondered" , "Contemplated" .)