Undistinguished little men (6)
I believe the answer is:
normal
'men' is the definition.
Although both the answer and definition are nouns, they are not in the same form of the noun.
'undistinguished little' is the wordplay.
'undistinguished' becomes 'norma' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'little' becomes 'l' (abbreviation).
'norma'+'l'='NORMAL'
Can you help me to learn more?
(Other definitions for normal that I've seen before include "Unexceptional" , "Ordinary, usual" , "Customary" , "Regular" , "Ordinary, not extraordinary" .)