IPA: /fæˈstɪdɪəsli/
KK: /fæˈstɪdɪəsli/
In a way that shows great attention to detail and accuracy, often being very careful about how things are done.
She fastidiously organized her notes before the exam.
Fastidiously → It is formed from "fastidium" (from Latin, meaning disgust or aversion) and the suffix "-ly" (meaning in a manner of). The word "fastidiously" means in a manner that shows aversion or excessive care about details.
Think of someone showing 'disgust' ('fastidium') and being very careful about how they do things — that's why fastidiously means doing something with great attention to detail.