monoatomic

US: (mon′ō ə tom′ik)

WordReference Random House Unabridged Dictionary of American English © 2026

mon•o•a•tom•ic  (mon′ō ə tom′ik), adj. [Chem.]

1. Chemistry monatomic.

Collins Concise English Dictionary © HarperCollins Publishers::

monoatomic / ˌmɒnəʊəˈtɒmɪk/ adjective

1. a variant of monatomic

WordReference Random House Unabridged Dictionary of American English © 2026

mon•a•tom•ic  (mon′ə tom′ik), adj. [Chem.]

1. Chemistry having one atom in the molecule.
2. Chemistry containing one replaceable atom or group.
3. Chemistry having a valence of one.

Also, monoatomic. 

• mon- + atomic 1840–50

mon′a•tom′i•cal•ly, adv. 

Collins Concise English Dictionary © HarperCollins Publishers::

monatomic / ˌmɒnəˈtɒmɪk/, monoatomic / ˌmɒnəʊəˈtɒmɪk/ adjective

1. (of an element) having or consisting of single atoms
2. (of a compound or molecule) having only one atom or group that can be replaced in a chemical reaction
3. a less common word for monovalent