Extremely sad (6)
I believe the answer is:
tragic
'extremely sad' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tragic that I've seen before include "Terrible" , "Extremely sad; Mahler's 6th nickname" , "Unfortunate" , "Very sad; Schubert's 4th symphony nickname" , "Involving grief of death or destruction" .)