Always uplifted after a key note (5)
I believe the answer is:
breve
'note' is the definition.
(musical note)
'always uplifted after a key' is the wordplay.
'always' becomes 'ever' (synonyms).
'uplifted' shows that the letters should be reversed in order.
'after' is a charade indicator (letters next to each other).
'a key' becomes 'b' (eg B major, musical key).
'ever' backwards is 'reve'.
'reve' put after 'b' is 'BREVE'.
(Other definitions for breve that I've seen before include "Long note (mus.)" , "Accent placed over a vowel" , "Note with the time value of eight crotchets" , "Rarely used musical note" , "(In music) long note" .)