Horrid smell from second fish (6)
I believe the answer is:
stench
'horrid smell' is the definition.
(I've seen this in another clue)
'second fish' is the wordplay.
'second' becomes 's' (common abbreviation).
'fish' becomes 'tench' (tench is a kind of fish).
's'+'tench'='STENCH'
'from' acts as a link.
(Other definitions for stench that I've seen before include "Nasty smell" , "A really vile smell" , "Offensive odour" , "Miasma" , "A really bad smell" .)