Voice ready to break bursting aloft (8)
I believe the answer is:
falsetto
'voice' is the definition.
(falsetto is a kind of voice)
'ready to break bursting aloft' is the wordplay.
'ready to' becomes 'set' ('set' can be a synonym of 'ready to').
'break' indicates putting letters inside.
'bursting' is an anagram indicator.
'aloft' is an anagram of 'falto'.
'set' put into 'falto' is 'FALSETTO'.
(Other definitions for falsetto that I've seen before include "it sounds high" , "Artificially high voice of latest sort" , "Artificially high voice tone" , "Artificially high voice pitch" , "Artificial upper register of a male voice" .)