Lake crossed by lady without equal (8)
I believe the answer is:
peerless
'without equal' is the definition.
('equal' can be 'peer' (synonyms) so maybe 'without equal' can be ''peerless')
'lake crossed by lady' is the wordplay.
'lake' becomes 'L' (geographical abbreviation).
'crossed by' is an insertion indicator (inserted letters are crossed or covered by others).
'lady' becomes 'peeress' (female peer).
'l' inserted into 'peeress' is 'PEERLESS'.
(Other definitions for peerless that I've seen before include "Outstanding" , "superb" , "Having no equals" , "Unique" , "Beyond compare" .)