Advertisement up and down quickly (4)
I believe the answer is:
gulp
'down quickly' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'advertisement up' is the wordplay.
'advertisement' becomes 'plug' (a plug is an advert for something).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'plug' backwards is 'GULP'.
'and' is the link.
Can you help me to learn more?
(Other definitions for gulp that I've seen before include "Swallow quickly" , "Swallow nervously" , "Audible swallow" , "Swallow hurriedly" , "Swallow noisily" .)