Stan may join him in India (5)
I believe the answer is:
hindu
'stan may join him' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'india' is the wordplay.
I cannot really understand how this works, but
'india' could be 'ind' (abbreviation) and 'ind' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'in' acts as a link.
Can you help me to learn more?
(Other definitions for hindu that I've seen before include "Native of India" , "Eastern believer" , "Religious believer" , "Most of the Indians are" , "Member of religious group" .)