When Scot joined Indian, say (5)
I believe the answer is:
asian
'indian say' is the definition.
(indian is a kind of Asian)
'when scot joined' is the wordplay.
'when' becomes 'as'.
'scot' becomes 'ian'.
'joined' is a charade indicator (letters next to each other).
'as'+'ian'='ASIAN'
(Other definitions for asian that I've seen before include "One from the East" , "florid writing" , "Thai or Iranian, perhaps?" , "Type of flu" , "From large continent" .)