Distributed key terribly late (5)
I believe the answer is:
dealt
'distributed' is the definition.
('deal' can be a synonym of 'distribute')
'key terribly late' is the wordplay.
'key' becomes 'd' (musical key).
'terribly' is an anagram indicator.
'late' is an anagram of 'ealt'.
'd'+'ealt'='DEALT'
(Other definitions for dealt that I've seen before include "Delivered" , "Carried out business" , "Distributed playing cards" , "Gave out playing cards" , "Traded" .)