Take top off - paunch not completely shaking (5)
I believe the answer is:
uncap
'take top off' is the definition.
(I've seen this before)
'paunch not completely shaking' is the wordplay.
'not completely' means to remove the last letter.
'shaking' is an anagram indicator.
'paunch' with its final letter taken away is 'paunc'.
'paunc' anagrammed gives 'UNCAP'.
(Other definitions for uncap that I've seen before include "Remove a cover from" , "Remove a top" , "open" , "Remove the lid" , "Take the top of the bottle" .)