Sailor Elizabeth became mother superior (6)
I believe the answer is:
abbess
'mother superior' is the definition.
(synonyms)
'sailor elizabeth' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'elizabeth' becomes 'Bess'.
'ab'+'bess'='ABBESS'
'became' acts as a link.
(Other definitions for abbess that I've seen before include "Mother superior" , "Head of convent" , "woman trying to be religious?" , "Head nun" , "She heads a religious community" .)