Tribe about to take most of country (4)
I believe the answer is:
clan
'tribe' is the definition.
(I know that tribe can be written as clan)
'about to take most of country' is the wordplay.
'about' becomes 'c' (abbreviation for circa).
'to take' is a charade indicator (letters next to each other).
'most of' means to remove the last letter.
'country' becomes 'land' (synonyms).
'land' with its final letter taken off is 'lan'.
'c'+'lan'='CLAN'
(Other definitions for clan that I've seen before include "Kinship group" , "Group with common ancestor, like the Campbells" , "Group of families with common ancestor" , "Group of related families" , "Extended family as in Scotland" .)