Wave, ready to accept quiet pupil (6)
I believe the answer is:
ripple
'wave' is the definition.
(I know that ripple is a type of wave)
'ready to accept quiet pupil' is the wordplay.
'ready' becomes 'ripe' (similar in meaning).
'to accept' means one lot of letters goes inside another.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'pupil' becomes 'L' (as in L-plates for a learner driver).
'p'+'l'='pl'
'ripe' enclosing 'pl' is 'RIPPLE'.
(Other definitions for ripple that I've seen before include "Slight disturbance on surface of lake" , "Small wave on a liquid's surface" , "Tiny wave; gentle applause" , "undulation" , "Edgar Allan ---, US author" .)