A sea chest, possibly? Possibly, possibly (2,3,4,3,2)
I believe the answer is:
as the case may be
'possibly' is the definition.
('as the case may be' means possibly or perhaps)
'a sea chest possibly? possibly' is the wordplay.
'possibly?' indicates anagramming the letters (I've seen 'possibly' mean this).
'possibly' becomes 'maybe' (synonyms).
'sea'+'chest'='seachest'
'seachest' with letters rearranged gives 'sthecase'.
'a'+'sthecase'+'maybe'='AS THE CASE MAY BE'
(Other definitions for as the case may be that I've seen before include "according to circumstances?" , "Accordingly" , "Carried on board or stored in hold" , "Open and shut, perhaps" , "according to how things turn out?" .)