Heather Lake's underwear (8)
I believe the answer is:
lingerie
'underwear' is the definition.
(lingerie is a kind of underwear)
'heather lake's' is the wordplay.
'heather' becomes 'ling' ('ling' can be a synonym of 'heather').
'lake' becomes 'erie' (Lake Erie is one of the Canadian/US 'Great Lakes').
'ling'+'erie'='LINGERIE'
(Other definitions for lingerie that I've seen before include "Women's underclothes" , "flimsy stuff" , "pants! Could be" , "CLOTHING" , "Slinky undergarments" .)