Legacies largely corrupt - sad (7)
I believe the answer is:
elegiac
'sad' is the definition.
(I've seen this before)
'legacies largely corrupt' is the wordplay.
'largely' means to remove the last letter.
'corrupt' indicates anagramming the letters.
'legacies' with its last letter removed is 'legacie'.
'legacie' is an anagram of 'ELEGIAC'.
(Other definitions for elegiac that I've seen before include "Thoughtful" , "Mournful, lamenting" , "Wistful, mournful" , "Funereal" , "Wistfully mournful" .)