1 [intransitive and transitive]
to make something sweeter, or become sweeter:
Sweeten the mixture with a little honey.
2 [transitive] also sweeten somebody ↔ up informal
to try to persuade someone to do what you want, by giving them presents or money or promising them something: ➔ sweetener (2)
a cash bonus to sweeten the deal
3 [transitive] literary
to make someone kinder, gentler etc:
Old age had not sweetened her.