One or two people playing (6)
I believe the answer is:
single
'one' is the definition.
(similar in meaning)
'two people playing' is the wordplay.
I cannot really understand how this works, but
'playing' could be 'in' and 'in' is found within the answer.
This explanation may well be incorrect...
'or' acts as a link.
Can you help me to learn more?
(Other definitions for single that I've seen before include "Ticket To Ride < : > hit" , "Just one - on one's own" , "Like bachelor" , "Sole" , "Unaccompanied" .)