Thin, as a voice (5)
I believe the answer is:
reedy
'thin as a voice' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for reedy that I've seen before include "Grassed up" , "Thin and piping" , "abounding with grasses" , "edge of some river-banks" , "Sounding thin - weak" .)