Second best finish (4)
I believe the answer is:
stop
'finish' is the definition.
('stop' can be a synonym of 'finish')
'second best' is the wordplay.
'second' becomes 's' (common abbreviation).
'best' becomes 'top' ('top' can be similar in meaning to 'best').
's'+'top'='STOP'
(Other definitions for stop that I've seen before include "It could be the organist's principal" , "Arrest" , "Red light signal" , "Halt; finish" , "Plug - organ knob - bus halt - period" .)