African unknown at house by Salvation Army (5)
I believe the answer is:
xhosa
'african' is the definition.
(the Xhosa are an African ethnic group)
'unknown at house by salvation army' is the wordplay.
'unknown' becomes 'x' (algebra).
'at' says to put letters next to each other.
'house' becomes 'ho' (abbreviation for house).
'by' says to put letters next to each other.
'salvation army' becomes 'SA' (abbreviation).
'x'+'ho'+'sa'='XHOSA'
(Other definitions for xhosa that I've seen before include "Member of a Bantu-speaking tribe" , "South African cattle-rearing people" , "Clicking tongue" , "South African language spoken with clicks" , "Cattle-rearer in South Africa" .)