Small circuit hit (4)
I believe the answer is:
slap
'hit' is the definition.
(thesaurus)
'small circuit' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'circuit' becomes 'lap' ('lap' can be a synonym of 'circuit').
's'+'lap'='SLAP'
(Other definitions for slap that I've seen before include "A blow among pals" , "Hit with a flat hand" , "Strike action" , "Mild punishment" , "Right" .)