Guest in capital of Vietnam is there regularly (7)
I believe the answer is:
invitee
'guest' is the definition.
('invitee' can be a synonym of 'guest')
'in capital of vietnam is there regularly' is the wordplay.
'capital of' suggests taking the first letters.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The initial letters of 'vietnam is' is 'vi'.
The alternating letters of 'there' are 'tee'.
'in'+'vi'+'tee'='INVITEE'
(Other definitions for invitee that I've seen before include "One asked to attend" , "visitor?" , "special guest" .)