One of the Great Lakes is spooky, we're told (4)
I believe the answer is:
erie
'one of the great lakes' is the definition.
(I've seen this in another clue)
'spooky we're told' is the wordplay.
'spooky' becomes 'eerie' (synonyms).
'we're told' indicates a 'sounds like' (homophone) clue.
'eerie' sounds like 'ERIE'.
'is' is the link.
(Other definitions for erie that I've seen before include "Lake between Canada and the US" , "N. American lake" , "Great lake in Eire" , "Superior companion" , "North american lake sounds spooky" .)