Musical effect is smooth, pervading warm feeling? Not entirely (9)
I believe the answer is:
glissando
'musical effect' is the definition.
(I've seen this before)
'is smooth pervading warm feeling? not entirely' is the wordplay.
I cannot really understand how this works, but
'is' is within the answer.
'smooth' could be 'sand' (sanding is a kind of smoothing) and 'sand' is present in the answer.
'not' could be 'o' (I've seen this in other clues) and 'o' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for glissando that I've seen before include "Musical flourish" , "Slide between two notes" , "Note with sliding pitch" , "note series rapidly executed" , "Re-interpreting this musical direction" .)