IPA: /ˈrænsɪdli/
KK: /ˈrænsɪdli/
In a way that has a strong, unpleasant smell or taste, often due to spoilage or decay.
The butter had gone rancidly, making the cookies taste terrible.
Rancidly → It is formed from "rancidus" (from Latin, meaning rotten or stinking) and the adverbial suffix "-ly" (meaning in a manner of). The word "rancidly" describes something that is in a manner of being rotten or having a foul smell.
Think of something that smells 'rotten' ('rancidus') to remember that 'rancidly' means having a foul smell.