Treated mercifully (6)
I believe the answer is:
spared
'treated mercifully' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for spared that I've seen before include "Avoided incurring" , "Let off by padres" , "Was merciful toward, refrained from harming" , "did without" , "Voluntarily parted with" .)