atom
nounUK /ˈætəm/
US /ˈætəm/
An atom is a very tiny piece of matter that everything is made of.
A water molecule is made of two hydrogen atoms and one oxygen atom.
OTHER MEANINGS
2. A very small amount of something.
There is not an atom of truth in that rumor.
3. The smallest unit of a chemical element that can exist.
Scientists split the atom in the twentieth century.
4. A tiny particle or dot.
Atoms of dust floated in the sunlight.