1 a : a very small piece of something
fine particles of sand
b : a very small amount of something
There is not a particle of evidence to support their claim.
There is not a particle of truth in what he said.
2 physics : any one of the very small parts of matter (such as a molecule, atom, or electron)
3 grammar : an adverb or preposition that when combined with a verb creates a phrasal verb
The phrasal verb “look up” consists of the verb “look” and the adverbial particle “up.”