101 Definition

wunōwun
noun
The essential facts or principles of a (specified) subject or activity.
A person who is ignorant of Flirting 101
Webster's New World
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adjective

(chiefly US, postpositive) Basic, beginner, starting from scratch.

Geology 101 tells us that you can't build a reservoir on sandstone.
Wiktionary
Synonyms:
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numeral

A thoroughly large number. Used especially in book titles.

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