Crossword Genius

Girl regularly leaves tough meat, finding fibre (5)

Ross

I believe the answer is:

istle

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

I don't understand the rest of the clue.

(Other definitions for istle that I've seen before include "Fibre from yucca or agave trees" , "for making nets?" , "Carpet material" .)

I've seen this clue in The Times.
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