Non-U sort of aluminium token (7)
I believe the answer is:
minimal
'token' is the definition.
(similar in meaning)
'non-u sort of aluminium' is the wordplay.
'non u sort of' becomes 'minim' (I can't justify this - if you can you should give a lot more credence to this answer).
'aluminium' becomes 'al' (chemical symbol).
'minim'+'al'='MINIMAL'
Can you help me to learn more?
(Other definitions for minimal that I've seen before include "Very small, the least possible (7)" , "Least possible; negligible" , "Of the least possible size" , "barely worth considering" , "Of a smallest amount" .)