Strange lake at the back of the house (5)
I believe the answer is:
eerie
'strange' is the definition.
(thesaurus)
'lake at the back of the house' is the wordplay.
'lake' becomes 'erie' (Lake Erie is one of the Canadian/US 'Great Lakes').
'at' means one lot of letters go next to another (I've seen this in other clues).
'the back of' suggests the final letters.
The last letter of 'house' is 'e'.
'erie' put after 'e' is 'EERIE'.
(Other definitions for eerie that I've seen before include "Strange and disturbing" , "Unnatural" , "Spectral" , "Scary, weird" , "Weird, uncanny" .)