Islander’s son with a complaint (6)
I believe the answer is:
samoan
'islander's' is the definition.
(I've seen this before)
'son with a complaint' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'with' says to put letters next to each other.
'complaint' becomes 'moan' (a moan is a complaint or objection).
's'+'a'+'moan'='SAMOAN'
(Other definitions for samoan that I've seen before include "from part of Polynesia" , "Islander" .)