Slowly, in play, followed some of Polonius's advice? (5)

I believe the answer is:

lento

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'slowly' is the definition.
(musical instruction)

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

(Other definitions for lento that I've seen before include "Slowly (mus.)" , "Slow (music)" , "Slow passage" , "(When playing music) slowly" , "(Of tempo) slow" .)

I've seen this clue in The Times.

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