a walking dictionary

A person who has a very large vocabulary or knows the definition of many words and who can recite them when asked. You should ask my brother what it means—he's a walking dictionary! Compared to most sixteen-year-olds, Sarah is a walking dictionary. She must read a lot in her spare time. What do I look like, a walking dictionary? How should I know how to spell "pneumococcal"?

a walking dictionary

a walking encyclopedia

If you describe someone as a walking dictionary or a walking encyclopedia, you mean that they know a lot of words or facts. She raised five of us on her own and she's a walking dictionary. He was a walking encyclopedia of music, full of wit and charm. Note: People sometimes use other words instead of dictionary or encyclopedia. He's a walking database on anything relating to insurance.

a walking ˈdictionary, encycloˈpedia, etc.

(informal) used to describe a human or living example of the thing mentioned: Geoff is a walking encyclopedia. He knows about everything. ♢ She’s a walking dictionary (= she knows a lot of words).