WWordGenerator.org GeneratorsWord ListsBlogAboutGenerate a word Home / M / mass number mass number noun 2 syllables 11 letters Scrabble 16 WWF 21 Definitions noun the sum of the number of neutrons and protons in an atomic nucleus nucleon number Look “mass number” up elsewhere Wiktionary ↗ Merriam-Webster ↗ Etymonline ↗ Dictionary.com ↗ Want another word?Spin the dictionary for a fresh one. Generate a word →