Second taxi delivering strike-breaker (4)
I believe the answer is:
scab
'strike-breaker' is the definition.
(I've seen this before)
'second taxi' is the wordplay.
'second' becomes 's' (common abbreviation).
'taxi' becomes 'cab' ('cab' can be a synonym of 'taxi').
's'+'cab'='SCAB'
'delivering' is the link.
(Other definitions for scab that I've seen before include "despicable person" , "He's not out" , "Ignorer of strike" , "Strike-breaker; skin disease in animals" , "Blackleg (colloq.)" .)