Artless native loses shirt (5)
I believe the answer is:
naive
'artless' is the definition.
(similar in meaning)
'native loses shirt' is the wordplay.
'loses' is a deletion indicator.
'shirt' becomes 't' (as in a T-shirt).
'native' with 't' removed is 'NAIVE'.
(Other definitions for naive that I've seen before include "Artless - green - ingenuous" , "Rather too simple and gullible" , "Artless, innocent" , "Simple in outlook" , "Inexperienced or gullible" .)