High-pitched (5)
'high-pitched' is the definition.
(similar in meaning)
This is the entire clue.
(Other definitions for shrill that I've seen before include "Keen" , "High and piercing" , "Of sound, piercing and high-pitched" , "Strident" , "(Of a cry) piercing" .)
(Other definitions for tinny that I've seen before include "Cheap" , "Made of poor metal" , "Lacking resonance" , "Aussie beer" , "With thin metallic sound" .)