One of the Furies (6)
I believe the answer is:
'one of the furies' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for alecto that I've seen before include "Fury exhibited" , "One of the Furies; locate (anag.)" , "One of classical Furies" , "A fury; locate (anag.)" , "Fury (Greek myth)" .)