who's who

American  

noun

1. a reference work containing short biographical entries on the outstanding persons in a country, industry, profession, etc..

   a who's who in automotive engineering.

2. the outstanding or influential persons in a community, industry, profession, or other group.

   The who's who of racing will be there.

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who's who British  

noun

1. a book or list containing the names and short biographies of famous people

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who's who Idioms  

1. The outstanding or best-known individuals of a group, as in Tonight's concert features a veritable who's who of musicians. This expression comes from the name of a famous reference work, Who's Who, first published in 1849, which contains biographical sketches of famous individuals and is regularly updated. Its name in turn was based on who is who, that is, the identity of each of a number of persons, a phrase dating from the late 1300s. [Early 1900s]

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Etymology

Origin of who's who

First recorded in 1840–50

Example Sentences

“So how does the system know who’s who? And when it flags someone — is it a human decision or just an algorithm flipping a switch?”

From Los Angeles Times • May 4, 2026

About 120 guests sardined into the modest backyard of Sonenshein’s Santa Monica childhood home, with a veritable who’s who of the L.A. restaurant scene doing double duty as attendees and vendors.

From Los Angeles Times • Apr. 28, 2026

The moment flag football was approved for the 2028 Olympics in Los Angeles, a who’s who of the NFL’s biggest stars all had the same reaction: We want in.

From The Wall Street Journal • Mar. 21, 2026

Kelly: We've also had a fair few people talk about being at your 40th birthday in January and it was like a who's who of football...

From BBC • Mar. 21, 2026

The names scratched into the posts no longer match the occupants, but I can extrapolate who’s who.

From "Water for Elephants" by Sara Gruen