IPA: /ˈswiːtənɪŋ/
KK: /ˈswitənɪŋ/
The process of making something sweet or adding sweetness to it.
The sweetening of the tea made it much more enjoyable.
Sweetening → It is formed from "sweet" (from Old English *swēte*, meaning having a pleasant taste) and "-ening" (a suffix indicating the process of making or becoming). The word "sweetening" refers to the process of making something sweet or enhancing its sweetness.
Think of something that is 'pleasant' ('sweet') becoming 'more' ('-ening') pleasant — that's what sweetening means.