Subject puts head in charge (5)
I believe the answer is:
topic
'subject' is the definition.
(as in a topic for discussion)
'head in charge' is the wordplay.
'head' becomes 'top' (synonyms).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'top'+'ic'='TOPIC'
'puts' acts as a link.
(Other definitions for topic that I've seen before include "Matter for an argument" , "That may be debatable" , "Subject (eg, of text)" , "might this be hot?" , "Theme of discourse" .)