Break after a day at sea (6)
I believe the answer is:
adrift
'at sea' is the definition.
(I've seen this before)
'break after a day' is the wordplay.
'break' becomes 'rift' (I've seen this before).
'after' says to put letters next to each other.
'a day' becomes 'ad' (I've seen this in other clues**).
'rift' put after 'ad' is 'ADRIFT'.
(Other definitions for adrift that I've seen before include "Wandering aimlessly" , "(Of boat) moving out of control" , "No longer fixed in position" , "Rudderless, astray" , "'Directionless, floating freely (6)'" .)