Innocent creature getting attorney to reveal Greek letter (6)
I believe the answer is:
lambda
'greek letter' is the definition.
(letter from the Greek alphabet)
'innocent creature getting attorney' is the wordplay.
'innocent creature' becomes 'lamb'.
'getting' is a charade indicator (letters next to each other).
'attorney' becomes 'DA' (District Attorney).
'lamb'+'da'='LAMBDA'
'to reveal' acts as a link.
(Other definitions for lambda that I've seen before include "Greek character" , "The 11th letter of the Greek alphabet" , "Teasing entertainer" , "Greek letter - am bald (anag)" , "Greek letter L" .)