Seaman with girl left rum (8)
I believe the answer is:
abnormal
'rum' is the definition.
(I've seen this before)
'seaman with girl left' is the wordplay.
'seaman' becomes 'ab' (short for able seaman).
'with' is a charade indicator (letters next to each other).
'girl' becomes 'norma' ().
'left' becomes 'l' (common abbreviation).
'ab'+'norma'+'l'='ABNORMAL'
(Other definitions for abnormal that I've seen before include "Odd" , "Unorthodox" , "Peculiar, unnatural" , "Highly unusual" , "Quite unusual" .)