Smooth, starts to sing awfully, needling daughter (4)
I believe the answer is:
Here is my best explanation:
'smooth' is the definition.
(sanding is a kind of smoothing)
'starts to sing awfully needling daughter' is the subsidiary indication.
'starts to' suggests taking the first letters.
'daughter' becomes 'd'.
The first letters of 'sing awfully needling' is 'san'.
(Other definitions for sand that I've seen before include "It's used to make glass", "Beach grains", "Grains of rock", "Beach constituent", "Dune constituent", "Seaside castle-building material", "Grains on beach", "Rub down (for painting)", "Grit; powdered rock" and "Beach grit".)