[verb] [T]The apple mixture can be sweetened with honey.(figurative) I think you should try to sweeten him (up) (= put him in a good mood) before you ask him for the loan. [M](figurative) The management sweetened the deal (= made it more attractive) by offering an extra 2% to staff on the lowest end of the pay scale.
SWEETEN
Meaning of SWEETEN in English
Cambridge English vocab. Кембриджский английский словарь. 2012