A cash reserve for moving aboard (6)
I believe the answer is:
afloat
'moving aboard' is the definition.
(afloat on the sea)
'a cash reserve' is the wordplay.
'cash reserve' becomes 'float' (cash used by a shop or trader).
'a'+'float'='AFLOAT'
'for' acts as a link.
(Other definitions for afloat that I've seen before include "On board a ship or boat" , "Out of debt; at sea" , "At sea, on the water" , "Resting on water" , "Buoyant: solvent" .)