Half-hearted physician with weapon (8)
I believe the answer is:
lukewarm
'half-hearted' is the definition.
(synonyms)
'physician with weapon' is the wordplay.
'physician' becomes 'luke' (I've seen this before).
'with' becomes 'w' (short for with).
'weapon' becomes 'arm' (synonyms).
'luke'+'w'+'arm'='LUKEWARM'
(Other definitions for lukewarm that I've seen before include "Tepid, or less than enthusiastic" , "Not enthusiastic like tepid water" , "Indifferent" , "Unenthusiastic" , "Half-hearted" .)