Radical former partner Mike wearing lime perhaps (7)
I believe the answer is:
extreme
'radical' is the definition.
(radical can mean revolutionary or extreme)
'former partner mike wearing lime perhaps' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'wearing' means one lot of letters goes inside another.
'lime perhaps' becomes 'tree' (lime is a kind of tree).
'm' going within 'tree' is 'treme'.
'ex'+'treme'='EXTREME'
(Other definitions for extreme that I've seen before include "Very great; not usual" , "Unrestrained" , "Very intense - way-out" , "Drastic -- limit" , "Far from moderate" .)