Crossword Genius

Chemical evidence of cannabis smoking? (6)

Ross

I believe the answer is:

potash

I'm a little stuck... Click here to teach me more about this clue!

This clue might be a double definition.

'chemical' is the first definition.
(I've seen this before)

'evidence of cannabis smoking?' is the second definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

Can you help me to learn more?

(Other definitions for potash that I've seen before include "Potassium compound used as fertiliser" , "Potassium carbonate or hydroxide" , "chemical compound" , "Alkaline compound" , "Strong alkali derived from burnt wood" .)

I've seen this clue in The Guardian and The Globe and Mail.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.