Weapon from the latter part of the Iron Age (6)
I believe the answer is:
'weapon' is the definition.
(I have seen 'ancient weapon' mean 'onager' so perhaps 'weapon' could also mean 'onager')
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for onager that I've seen before include "Asian wild ass - orange (anag)" , "Asiatic wild ass" , "wild beast" , "The ass is a strange orange" , "Strangely, the wild ass might be orange" .)