# Planck's constant

> English word · Proper noun

## Definitions
1. the constant of proportionality (symbol ℎ), relating the energy and frequency of a photon (6.626×10⁻³⁴ joule-second); also related to the indeterminacy limit in the Heisenberg uncertainty principle; the quantum of action

## Etymology
Named for Max Planck (1858–1947), German theoretical physicist, who discovered it in 1900.

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