One leading 1000 very good warriors (4)
I believe the answer is:
impi
'warriors' is the definition.
(I've seen this before)
'one leading 1000 very good' is the wordplay.
'one' becomes 'i' (Roman numeral).
'leading' is a charade indicator (letters next to each other).
'p000' becomes 'M' (synonyms).
'very good' becomes 'pi' (I've seen this in other clues).
'i'+'m'+'pi'='IMPI'
(Other definitions for impi that I've seen before include "warrior band" , "Old warriors" , "armed warriors" , "Group of Bantu warriors" , "Body of Zulu warriors" .)