Impale second fish (5)
I believe the answer is:
spike
'impale' is the definition.
('spike' can be a synonym of 'impale')
'second fish' is the wordplay.
'second' becomes 's' (common abbreviation).
'fish' becomes 'pike' (pike is a kind of fish).
's'+'pike'='SPIKE'
(Other definitions for spike that I've seen before include "one that may be found on running shoe" , "Anglo-Catholic comedian" , "spear" , "add something to it" , "Frustrate" .)