Might Ernst & Young watch out at last for corruption? (8)
I believe the answer is:
strength
'might' is the definition.
(I've seen this before)
'ernst young watch out at last for corruption?' is the wordplay.
'at last' indicates one should take the final letters.
'for corruption?' is an anagram indicator (I've seen 'for corruption' mean this (I've seen this in other clues)).
The final letters of 'young watch out' are 'ght'.
'ernst'+'ght'='ernstght'
'ernstght' is an anagram of 'STRENGTH'.
(Other definitions for strength that I've seen before include "Force, might, potency" , "The longest one-syllable word in English - might" , "A good quality; might" , "Concentration" , "Force, firmness" .)