Fellows suppressing wrong number, keeping one hidden for a long time (10)
I believe the answer is:
millennium
'a long time' is the definition.
(a millennium is a thousand years)
'fellows suppressing wrong number keeping one hidden' is the wordplay.
I cannot quite see how this works, but
'wrong' could be 'ill' (I've seen this in another clue) and 'ill' is present in the answer.
'fellows' could be 'men' (fellow can mean a man) and 'men' is found in the leftover letters.
'number' could be 'm' (M is an example) and 'm' is found within the answer.
'one' could be 'i' (Roman numeral) and 'i' is found in the answer.
The remaining letters 'nu' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'for' acts as a link.
Can you help me to learn more?
(Other definitions for millennium that I've seen before include "1,000 years" , "Period of one thousand years" , "age" .)