Thin and high-pitched (5)
I believe the answer is:
reedy
'thin and high-pitched' 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 "(Of voice) high/thin" , "edge of some river-banks" , "Like oboe's sound?" , "(Of sound) high and thin" , "Long and thin" .)