Deep, as a voice (3)
I believe the answer is:
low
'deep as a voice' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for low that I've seen before include "Make a cow-like noise" , "Deep sound of cattle - not high" , "Unimportant sort of owl" , "Depressed; near the ground" , "Not high or tall" .)