Close second to peloton's leader (4)
I believe the answer is:
stop
'close' is the definition.
(thesaurus)
'second to peloton's leader' is the wordplay.
'second' becomes 's' (common abbreviation).
'leader' says to take the initial letters.
The first letter of 'peloton' is 'p'.
's'+'to'+'p'='STOP'
(Other definitions for stop that I've seen before include "Withhold large amount raised" , "Halt; finish" , "Come to a halt" , "Plug - organ knob - bus halt - period" , "Standstill" .)