By a large lake Heather slips maybe (8)
I believe the answer is:
lingerie
'slips maybe' is the definition.
(slip is a type of lingerie)
'by a large lake heather' is the wordplay.
'by' means one lot of letters go next to another.
'a large lake' becomes 'Erie' (one of the Great Lakes).
'heather' becomes 'ling' (synonyms).
'erie' after 'ling' is 'LINGERIE'.
(Other definitions for lingerie that I've seen before include "One from W Atlantic island group" , "Women's underwear and nightwear" , "pants! Could be" , "stockings, say?" , "Slinky undergarments" .)