# mass number

> English word · Noun

## Definitions
1. The total number of protons and neutrons in an atomic nucleus. Symbol: A

## Etymology
Ellipsis of atomic mass number.

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