Regularly lobby meeting with passion (9)
I believe the answer is:
obsession
'passion' is the definition.
(thesaurus)
'regularly lobby meeting' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'meeting' becomes 'session' (session is a kind of meeting).
The alternating letters of 'lobby' are 'ob'.
'ob'+'session'='OBSESSION'
'with' acts as a link.
(Other definitions for obsession that I've seen before include "Continual preoccupation" , "Thing" , "All-absorbing idea" , "Persistent preoccupation" , "All-consuming idea" .)