Endlessly short-tempered, note (8)
I believe the answer is:
crotchet
'note' is the definition.
(crotchet is a kind of note)
'endlessly short-tempered' is the wordplay.
'endlessly' means to remove the last letter.
'short-tempered' becomes 'crotchety' (I've seen this before).
'crotchety' with its last letter taken away is 'CROTCHET'.
(Other definitions for crotchet that I've seen before include "Musical note equal to half a minim" , "perverse notion" , "In music, it has quarter the time value of a whole note" , "Two quavers as one note" , "One in bar" .)