Second unlikely delay (5)
I believe the answer is:
stall
'delay' is the definition.
(stalling is a kind of delaying)
'second unlikely' is the wordplay.
'second' becomes 's' (common abbreviation).
'unlikely' becomes 'tall' (I've seen this in other clues).
's'+'tall'='STALL'
(Other definitions for stall that I've seen before include "Come to a halt" , "Be evasive" , "Part of the stable" , "(Of engine) stop running; booth" , "Booth; prevaricate" .)