Crossword Genius

A little one to many (4)


I believe the answer is:

'a little' is the definition.

'one to many' is the wordplay.
'one' becomes 'a'.
'many' becomes 'm' ().

(Other definitions for atom that I've seen before include "ounce", "Smallest particle in an element able to take part in a chemical reaction", "A small but mighty particle", "Smallest amount", "A wee bit".)