the.com/sweetener

means Something extra — money, a perk, or an artificial substance — added to make a deal, drink, or offer more appealing than it honestly is.

from Straightforward join of 'sweeten' (make sweet) plus the agent suffix '-er,' from Old English swēte, related to Latin suavis (pleasant). The literal sense — a substance that sweetens food or drink — is old and plain; the figurative sense, an inducement slipped into a deal to make it go down easier, grew naturally once people noticed that sugar and bribery work by the same basic principle.