Spirit? No alcoholic drink to be knocked back (6)
I believe the answer is:
daemon
'spirit?' is the definition.
(I know that daemon is a type of evil spirit)
'no alcoholic drink to be knocked back' is the wordplay.
'alcoholic drink' becomes 'mead' (I've seen this before).
'to be knocked back' is a reversal indicator.
'no'+'mead'='nomead'
'nomead' in reverse letter order is 'DAEMON'.
(Other definitions for daemon that I've seen before include "guardian spirit" , "Spirit in ancient Greek belief" , "Evil spirit" .)