Maven
Etymology
From Yiddish meyvn, from Hebrew mēvīn (“one who understands,” from the root b-y-n, “to understand”). It spread in American English partly through advertising in the 1960s and names not just an expert but an eager, sharing one.
noun · /MAY-vuhn/
A knowledgeable enthusiast whom others turn to for trusted advice on a subject.
What it names
The go-to person in a niche — the friend who has read every review and genuinely delights in telling you which one to buy.
Example
Ask the office coffee maven — she can tell you the roast date from a single sip.
Related idea
An expert has deep knowledge; a maven is an enthusiast others rely on, especially one who loves passing what they know along.