One inhabiting island, part of Asia Minor (5)
I believe the answer is:
ionia
'part of asia minor' is the definition.
(I know this)
'one inhabiting island' is the wordplay.
'one' becomes 'I' (Roman numeral).
'inhabiting' indicates putting letters inside (I've seen this in other clues).
'island' becomes 'iona' (Scottish island).
'i' put inside 'iona' is 'IONIA'.
(Other definitions for ionia that I've seen before include "Classical Aegean region" , "part of Asia Minor" , "Ancient area" , "Old territory" , "ancient region of Eastern Mediterranean" .)