Good-natured sort left legacy behind (6)
I believe the answer is:
kindly
'good-natured' is the definition.
(thesaurus)
'sort left legacy behind' is the wordplay.
'sort' becomes 'kind' ('kind' can be a synonym of 'sort'**).
'left' becomes 'l' (common abbreviation).
'behind' suggests the final letters.
The final letter of 'legacy' is 'y'.
'kind'+'l'+'y'='KINDLY'
(Other definitions for kindly that I've seen before include "Benign" , "Beneficent - please" , "Benevolent - please!" , "Please; considerate" , "Charitable, good-hearted" .)