Endlessly sneered - resorted to calm (6)
I believe the answer is:
serene
'calm' is the definition.
(synonyms)
'endlessly sneered resorted' is the wordplay.
'endlessly' means to remove the last letter.
'resorted' indicates anagramming the letters.
'sneered' with its last letter taken off is 'sneere'.
'sneere' anagrammed gives 'SERENE'.
'to' acts as a link.
(Other definitions for serene that I've seen before include "Peaceful and unruffled" , "Not agitated" , "Impassive" , "Calm, peaceful, tranquil" , "Calm, untroubled" .)