Head discovered vice is matter for debate (5)
I believe the answer is:
topic
'matter for debate' is the definition.
'topic' can be an answer for 'matter' (I've seen this in another clue). I'm not sure about the 'for debate' bit.
'head discovered vice' is the wordplay.
'head' becomes 'top' (synonyms).
'discovered' indicates the central letters (dis-covered - outer letters removed).
The centre of 'vice' is 'ic'.
'top'+'ic'='TOPIC'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for topic that I've seen before include "Subject (of speech, etc)" , "Talking point" , "A subject for conversation or debate" , "Issue (for discussion)" , "Question" .)