Infant born before sailor gets by in the end (4)
I believe the answer is:
baby
'infant' is the definition.
(synonyms)
'born before sailor gets by in the end' is the wordplay.
'born' becomes 'b'.
'before' is a charade indicator (letters next to each other).
'sailor' becomes 'ab' (abbreviation for able seaman).
'gets' is a charade indicator (letters next to each other).
'in the end' suggests the final letters.
The final letter of 'by' is 'y'.
'b'+'ab'+'y'='BABY'
(Other definitions for baby that I've seen before include "Very young child" , "Infant" , "Pet project" , "Small child" , "invention" .)