/ Dictionary / Index A atomicity: Meaning and Definition of Find definitions for: at•o•mic•i•ty Pronunciation: (at"u-mis'i-tē), [key] — n. Chem. the number of atoms in a molecule of a gas. valence. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. atomic hydrogen atomic mass Related Content Daily Word Quiz: crutiny Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language