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' says the answer is hidden in the clue.
'NORSE' can be found hidden inside '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)" .)