They strum quietly before tragic heroine executed (7)

I believe the answer is:

plectra

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'they' is the definition.
Both the answer and definition are plural nouns.
Perhaps there's an association between them I don't understand?

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

Can you help me to learn more?

(Other definitions for plectra that I've seen before include "Parts for harpsichord" , "Bits of plastic maybe" , "Guitar plucking aids" , "Guitar pickers - carp let (anag)" , "Guitar picks" .)

I've seen this clue in The Guardian.

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