Viking taking part in invasion or settlement (5)
I believe the answer is:
norse
'viking' is the definition.
(the Vikings were a Norse people)
'part in invasion or settlement' is the wordplay.
'part in' indicates a hidden word.
'NORSE' is hidden in the letters of 'invasion or settlement'.
'taking' acts as a link.
(Other definitions for norse that I've seen before include "Native to Norway" , "Old form of Norwegian" , "Relating to Norway" , "Old European" , "Language - senor! (anag)" .)