Forging alibi with ' a cold' - wicked! (10)
I believe the answer is:
diabolical
'wicked' is the definition.
('diabolical' can be similar in meaning to 'wicked')
'forging alibi with a cold' is the subsidiary indication.
'forging' is an anagram indicator (I've seen this in other clues).
'with ' is a charade indicator (letters next to each other).
'a'+'cold'='acold'
'alibi' after 'acold' is 'acoldalibi'.
'acoldalibi' with letters rearranged gives 'diabolical'.
(Other definitions for diabolical that I've seen before include "Demonic" , "evil" , "Disgraceful" , "Fiendish" , "Absolute" .)