Meaning of ATOM in English

at ‧ om /ˈætəm/ BrE AmE noun [countable]

[ Date: 1500-1600 ; Language: Latin ; Origin: atomus , from Greek , from atomos 'that cannot be divided' , from temnein 'to cut' ]

1 . the smallest part of an ↑ element that can exist alone or can combine with other substances to form a ↑ molecule :

carbon atoms

atom of

two atoms of hydrogen

2 . a very small amount of something – used for emphasis

atom of

There isn’t an atom of truth in it.

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.