One way to hold this word: something is hard to swallow, so a small sweet thing goes in alongside it. That is the whole word. In a cup it is the spoon of honey or the tiny tablet that replaces sugar. On a desk it is the free year of service dropped into a contract nobody wanted to sign. The thing being swallowed does not change; what changes is how easily it goes down.
From the verb sweeten plus the agent suffix -er: the thing that does the sweetening, like opener or cleaner.
由動詞 sweeten（使變甜）加上表示「做這件事的人或東西」的字尾 -er 組成，跟 opener、cleaner 同一個造法。字面就是「負責把東西弄甜的那個」。這條線索也說明了為什麼它後來可以離開廚房：只要有東西需要被弄得好接受一點，那個角色就是 sweetener。
Wiktionary entry supplied in this batch's evidence packet (source_ref kaikki:3f6f69a190036ae4:886316490)
Two branches
讓食物變甜的東西
核心畫面最字面的一半：真的放進嘴裡的那一點甜。
noun · B1
Something you put into food or drink to make it taste sweeter. It usually means a substance used in place of sugar, such as the ones in diet drinks, but it can also cover natural sweet things like honey.
甜味劑
讓一筆交易變得好接受的東西
同一個動作換了桌子：原本是食物不好入口，現在是條件不好接受，於是一樣先加一點甜的進去。
noun · C1
Something extra that you offer someone so that they will agree to something, especially a business deal. It can be an open extra, such as a discount or a free service, and it can also be money paid quietly to buy someone's agreement.
甜頭