The sailor has to put back a card (5)
I believe the answer is:
tarot
'a card' is the definition.
(tarot cards are used to tell fortunes)
'the sailor has to put back' is the wordplay.
'the sailor' becomes 'tar' (tar can mean a sailor).
'has' is a charade indicator (letters next to each other).
'put back' is a reversal indicator.
'to' backwards is 'ot'.
'tar'+'ot'='TAROT'
(Other definitions for tarot that I've seen before include "Sort of cards" , "Fortune teller's seventy eight card pack" , "Arcana cards" , "Set of cards used by fortune-tellers" , "Pack of cards used in fortune-telling" .)