The first person on a Scottish isle (4)
I believe the answer is:
iona
'scottish isle' is the definition.
(I've seen this in another clue)
'the first person on a' is the wordplay.
'the first person' becomes 'I' ('I' is a first-person pronoun).
'i'+'on'+'a'='IONA'
(Other definitions for iona that I've seen before include "Inner Hebridean island" , "holy site" , "Scottish island from where Christianity spread in 563 AD" , "St Columba's island of the Inner Hebrides" , "part of Scotland" .)