# E=mc²

> English word · Noun · IPA /ˈiː ˌiːkwəlz ɛm siː ˈskwɛːd/

## Definitions
1. A formulation or realization that captures a profound thought in simple terms.
2. Used other than figuratively or idiomatically: E = mc²: energy equals mass times the speed of light's square.

## Etymology
After the formula of mass–energy equivalence, an important principle discovered by the German-born theoretical physicist Albert Einstein (1879–1955).
The formula entered the popular consciousness after it was included in the opening pages of the Smyth Report (1945), a widely read document that explained the United States’ nuclear weapons program to the public for the first time. Its appearance alongside a portrait of the (already well known) Einstein on a Time magazine cover the following year consolidated its fame.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/e-mc