Take down or plug up (4)
I believe the answer is:
gulp
'take down' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'plug up' is the wordplay.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'plug' written backwards gives 'GULP'.
'or' is the link.
Can you help me to learn more?
(Other definitions for gulp that I've seen before include "Swallow in large mouthfuls" , "Audible swallow" , "Noise made when swallowing too quickly" , "Swallow nervously" , "Swallow audibly" .)