Strange sailor girl on lake (8)
I believe the answer is:
abnormal
'strange' is the definition.
(both can mean unusual)
'sailor girl on lake' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'girl' becomes 'norma' ().
'on' means one lot of letters go next to another.
'lake' becomes 'L' (geographical abbreviation).
'ab'+'norma'+'l'='ABNORMAL'
(Other definitions for abnormal that I've seen before include "Rum" , "Different to what is ordinary or expected" , "Extraordinary" , "Moral ban (anag.)" , "'Aberrant, atypical (8)'" .)