Definition of sweetens:
(v) :
(transitive) To make sweet to the taste.
(v) :
(transitive) To make (more) pleasant or to the mind or feelings.
(v) :
(transitive) To make mild or kind; to soften.
(v) :
(transitive) To make less painful or laborious; to relieve.
(v) :
(transitive) To soften to the eye; to make delicate.
(v) :
(transitive) To make more attractive; said of offers in negotiations.