Lake that is part of a series (4)
I believe the answer is:
erie
'lake' is the definition.
(Lake Erie is one of the Canadian/US 'Great Lakes')
'part of a series' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'ERIE' can be found hidden inside 'series'.
'that is' is the link.
(Other definitions for erie that I've seen before include "Superior companion" , "The lake sounds weird" , "North american lake sounds spooky" , "A Great American lake - sounds spooky" , "Great lake in Eire" .)