Please go in that inn regularly (9)
I believe the answer is:
entertain
'please' is the definition.
(thesaurus)
'go in that inn regularly' is the wordplay.
'go in' becomes 'enter' ('enter' can be a synonym of 'go in').
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'that'+'inn'='thatinn'
The alternate letters of 'thatinn' are 'tain'.
'enter'+'tain'='ENTERTAIN'
(Other definitions for entertain that I've seen before include "harbour" , "Create a diversion" , "Amuse - give hospitality" , "cheer" , "Have company" .)