sweetener

noun

1. Something added to food to sweeten its taste, especially an artificial substitute for sugar.

   “Some examples of the sweeteners include aspartame, saccharin, sucralose and stevia. The W.H.O.’s announcement contradicts previous studies that have said these sweeteners don’t offer any health benefits but also do not cause harm.”

   “Even as FDA works to develop that plan, consumers continue to be exposed to unsafe food chemicals including not just dyes but also the artificial sweetener aspartame, the white pigment titanium dioxide, the preservative propylparaben, and the phthalate food packaging chemicals, according to CSPI.”

2. (informal)Something given or added to a deal to sweeten another's attitude, especially a bribe or kickback.
3. (slang)A shill bidder at an auction.