which is which

Idioms

What particular one is what particular one, or what is the difference between different ones. For example, These twins look so much alike I can't tell which is which, or Both our raincoats are tan; do you know which is which? This idiom was first recorded about 1412.

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

Knowing which is which can save you a surprising amount of December stress.

From Salon • Dec. 23, 2025

The detection process is time-consuming for human observers - but Squirrel Agent uses the power of AI to rapidly analyse all those markers and decide with an extremely high level of accuracy which is which.

From BBC • Nov. 23, 2024

And how does Google Maps determine which is which?

From Slate • Oct. 26, 2023

Fact, fiction and conspiracy blur together until you can’t tell which is which, and you almost cease to care.

From Los Angeles Times • Sep. 8, 2023

I can’t tell which is which, because they’re the muscle.

From "The Inquisitor's Tale" by Adam Gidwitz

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023