Slasher presumably showing vamp with a different origin (7)
I believe the answer is:
reducer
'origin' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for reducer that I've seen before include "that has a weakening effect?" , "One making weaker" , "Piece for joining pipes of differing diameter" , "Agent used when developing" , "I get less" .)