Stamp of approval (4)
'stamp of approval' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for seal that I've seen before include "Sea-dweller can produce a wax impression" , "Member of an elite force within the US Navy" , "Signet" , "Amphibious sea animal or kind of stamp" , "Wax stamp" .)
(Other definitions for accepted that I've seen before include "Conventional -- customary" , "Believed to be valid" , "Established" , "Agreed to receive, or approved" , "Said 'yes'" .)