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

The donors are a who’s who of tech leaders, venture capitalists and other leaders in the gig, gaming, digital media and AI defense fields.

From Los Angeles Times • May 18, 2026

In the comments section of Skylight’s post announcing the big news, the who’s who of L.A.’s literati popped the proverbial champagne.

From Los Angeles Times • Apr. 16, 2026

"He knows my players, he's well aware of who's who, and some of them still can't get their head around that when I tell them."

From Barron's • Feb. 25, 2026

As for the presenters, it's a who's who of famous names, led by none other than Paddington Bear.

From BBC • Feb. 21, 2026

I only know who’s who because each of us is labeled.

From "Zara’s Rules for Record-Breaking Fun" by Hena Khan