North American Indian, 100, about last of tribe (4)
I believe the answer is:
cree
'north american indian' is the definition.
(I've seen this before)
'100 about last of tribe' is the wordplay.
'r00' becomes 'c' (roman numeral).
'about' becomes 're' (regarding**).
'last of' indicates one should take the final letters.
The last letter of 'tribe' is 'e'.
'c'+'re'+'e'='CREE'
(Other definitions for cree that I've seen before include "Native American tribe/language" , "tribe" , "American Indians" , "Native American; rhymes with French cheese" , "North American native" .)