Having mixed it, threw it out (8)
I believe the answer is:
scrapped
'out' is the definition.
The answer and definition are not the same part of speech. However, adjectives and past participle verbs can sometimes define each other.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for scrapped that I've seen before include "Put up fight" , "Abolished, cancelled" , "Discarded as useless" , "abandoned in a heap?" , "Fought - ceased to use" .)