Hide missing note: it’s froth (6)
I believe the answer is:
lather
This might be a double definition.
'hide missing note' is the first definition.
'lather' can be an answer for 'hide' (thesaurus). I am unsure of the 'missing note' bit.
'froth' is the second definition.
(lathering is a kind of frothing)
'it's' is the link.
Can you help me to learn more?
(Other definitions for lather that I've seen before include "Froth produced by soap" , "Whip up froth - tizzy" , "Froth formed by soap and water" , "starting to run in a sweat" , "Foam - tizzy (informal)" .)