Weapon - injure about one thousand with it (8)
I believe the answer is:
scimitar
'weapon' is the definition.
(scimitar is a kind of weapon)
'injure about one thousand with it' is the wordplay.
'injure' becomes 'scar' (I've seen this in other clues).
'about' is an insertion indicator.
'one thousand with' becomes 'im' (I can't justify this - if you can you should give a lot more credence to this answer).
'im'+'it'='imit'
'scar' going around 'imit' is 'SCIMITAR'.
Can you help me to learn more?
(Other definitions for scimitar that I've seen before include "Double-edged sword" , "I'm racist, owning an oriental sword" , "Steel" , "Sword with curved blade used by the Turks and Persians" , "sharp weapon" .)