Innocent Greek character killed, sadly (9)
I believe the answer is:
childlike
'innocent' is the definition.
(I've seen this before)
'greek character killed sadly' is the wordplay.
'greek character' becomes 'chi' (letter from the Greek alphabet).
'sadly' indicates anagramming the letters.
'killed' is an anagram of 'ldlike'.
'chi'+'ldlike'='CHILDLIKE'
(Other definitions for childlike that I've seen before include "Innocent and trustful?" , "unsophisticated" , "Showing youthful innocence" , "Having the innocence of extreme youth" .)