Crossword Genius

Pair of old ladies maintaining this compiler stinks! (7)

Ross

I believe the answer is:

miasmas

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

'stinks' is the definition.
Although both the answer and definition are plural nouns, I don't understand how one could define the other.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Another definition for miasmas that I've seen is " unpleasant atmospheres".)

I've seen this clue in The Guardian.
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