Performing hound circling pub endlessly (5)
I believe the answer is:
doing
'performing' is the definition.
('do' can be a synonym of 'perform')
'hound circling pub endlessly' is the wordplay.
'hound' becomes 'dog' (synonyms).
'circling' indicates putting letters inside (circling can mean going around or containing).
'pub' becomes 'inn' (an inn is a type of pub).
'endlessly' means to remove the last letter.
'inn' with its last letter taken away is 'in'.
'dog' placed around 'in' is 'DOING'.
(Other definitions for doing that I've seen before include "Hoaxing" , "visiting as a tourist" , "Effecting" , "Beating (colloquial); performing" , "Accomplishing" .)