Odd seaman with girl on lake (8)
I believe the answer is:
abnormal
'odd' is the definition.
(I've seen this in another clue)
'seaman with girl on lake' is the wordplay.
'seaman' becomes 'ab' (short for able seaman).
'with' means one lot of letters go next to another.
'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 "Irregular" , "Different to what is ordinary or expected" , "Moral ban (anag.)" , "Deviating from the standard" , "Deviant, different from the usual" .)