Husband to Mathilde perhaps housing old south sea islander (5)
I believe the answer is:
maori
'south sea islander' is the definition.
(the Maori are the aboriginal people of New Zealand)
'husband to mathilde perhaps housing old' is the wordplay.
'husband to mathilde perhaps' becomes 'mari' ('husband' in French - Mathilde is a French name).
'housing' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'mari' enclosing 'o' is 'MAORI'.
(Other definitions for maori that I've seen before include "race" , "Polynesian aboriginal" , "Native language of NZ" , "Pa may accommodate one" , "I roam (anag)" .)