Smallest of the Great Lakes (7)
I believe the answer is:
ontario
'smallest of the great lakes' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ontario that I've seen before include "Province of SE Canada, and a Great Lake" , "Canadian province and Great Lake" , "one of the provinces" , "part of N America" , "vast lake" .)