Believer taking month to cross India (4)
I believe the answer is:
jain
'believer' is the definition.
(believer in Jainism)
'month to cross india' is the wordplay.
'month' becomes 'jan' (Jan is short for January).
'to cross' means one lot of letters goes inside another (some letters cross or go round others).
'india' becomes 'i' (phonetic alphabet: alpha, bravo, charlie etc.).
'jan' placed around 'i' is 'JAIN'.
'taking' is the link.
(Other definitions for jain that I've seen before include "Member of Indian sect" , "Follower of an Indian religion" , "adherent of an Indian religion" , "religious Indian" .)