Stop up (4)
There are a few possibilities for this:
'stop up' 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 "Marine animal or sign of authenticity" , "Signet" , "Close - (performing?) animal" , "Amphibious fish-eating sea mammal" , "stop leaks" .)
(Other definitions for tamp that I've seen before include "press down firmly" , "Press down tightly" , "Pat firmly (down)" , "Pack or ram down tightly" , "Pack, force down" .)
'stop up' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for clog that I've seen before include "Bung up" , "Obstruct the wooden shoe" , "Block up - type of shoe" , "Congest" , "Become blocked with wooden-soled shoe" .)
'stop up' is the definition.
(I know that stop up can be written as plug)
This is the entire clue.
(Other definitions for plug that I've seen before include "Piece of chewing tobacco" , "Publicise -- stop" , "Stop - advertising" , "See 19" , "Stopper - publicise" .)