Slowly, in play, followed some of Polonius's advice? (5)
I believe the answer is:
lento
'slowly' is the definition.
(musical instruction)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for lento that I've seen before include "Slowly (mus.)" , "Slow (music)" , "Slow passage" , "(When playing music) slowly" , "(Of tempo) slow" .)