The one to right of them (5)
I believe the answer is:
their
'of them' is the definition.
(I've seen this before)
'the one to right' is the wordplay.
'the one' becomes 'thei' (I am not sure about this - if you are sure you should believe this answer much more).
'to right' becomes 'r' (common abbreviation).
'thei'+'r'='THEIR'
Can you help me to learn more?
(Other definitions for their that I've seen before include "Possessive pronoun" , "Some would say his (or her)" , "Belonging to him (perhaps wrongly)" , "belonging to an individual" , "Those people's" .)