noun

1. A very small piece of matter, a fragment; especially, the smallest possible part of something.

2. Any of various physical objects making up the constituent parts of an atom; an elementary particle or subatomic particle.

3. A word that has a particular grammatical function but does not obviously belong to any particular part of speech, such as the word to in English infinitives or O as a vocative particle.

Synonyms: p-word