To make (more) pleasant or to the mind or feelings.
to sweeten life
to sweeten friendship
3
To make mild or kind; to soften.
to sweeten the temper
4
To make less painful or laborious; to relieve.
to sweeten the cares of life
Our God to bless out home delights, / And sweeten every secret tear:— [...]
5
To soften to the eye; to make delicate.
Correggio has made his memory immortal by the strength he has given to his figures, and by sweetening his lights and shadows, and melting them into each other.