Large sea bird (9)
I believe the answer is:
albatross
'large sea bird' is the definition.
(I know that albatross are big)
This is the entire clue.
(Other definitions for albatross that I've seen before include "Large seabird found among lost Arabs" , "Atlas bros alter the large bird with narrow wings" , "As Borstal is adapted for a big bird" , "Great hole" , "Large seabird or constant burden" .)