Sailor's fallen into the sea — not entirely sober, to be honest (5,5)
I believe the answer is:
above board
'honest' is the definition.
(I've seen this before)
'sailor's fallen into the sea not entirely sober' is the wordplay.
I cannot quite understand how this works, but
'not' could be 'o' (I've seen this in other clues) and 'o' is found in the answer.
'sailor' could be 'ab' (abbreviation for able seaman) and 'ab' is found in the answer.
This explanation may well be incorrect...
'to be' is the link.
Can you help me to learn more?
(Other definitions for above board that I've seen before include "like a successful surfer?" , "Entirely honest" , "at the top of the table?" , "MD is" , "OK?" .)