Our brief to be welcomed by half a dozen native Americans (5)
I believe the answer is:
sioux
'native americans' is the definition.
(the Sioux are a Native American people)
'our brief to be welcomed by half a dozen' is the wordplay.
'brief' means to remove the last letter (a shorter or briefer version of the word).
'to be welcomed by' indicates putting letters inside (letters welcomed inside).
'half a dozen' becomes 'six' (synonyms).
'our' with its last letter taken off is 'ou'.
'ou' going into 'six' is 'SIOUX'.
(Other definitions for sioux that I've seen before include "in Dakota" , "Native American people" , "Native Indian group" , "Native American from between Lake Michigan and the Rockies" , "Sitting Bull's people" .)