sweeten
v.to make something more pleasant or attractive by adding something good to it. You can use this for food, music, or even a deal.
v.to make something more agreeable or attractive by adding a desirable element. Often used figuratively in business or music contexts to describe improving a deal or a sound.
“The company decided to sweeten the deal by offering a free holiday.”
“The band added a few extra guitar solos to sweeten the sound of their new album.”
“While the initial terms of the merger were unfavorable, the board voted to sweeten the offer by including stock options to ensure the acquisition's success.”
From sweet + -en. Eclipsed non-native Middle English doucen and endoucen, borrowed from Old French adoucir and endoucir (“to sweeten”).
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.