a minute portion, piece, fragment, or amount; a tiny or very small bit: a particle of dust; not a particle of supporting evidence.
Physics. one of the extremely small constituents of matter, as an atom or nucleus. an elementary particle, quark, or gluon. a body in which the internal motion is negligible.
a clause or article, as of a document.
Grammar. (in some languages) one of the major form classes, or parts of speech, consisting of words that are neither nouns nor verbs, or of all uninflected words, or the like. such a word. a small word of functional or relational use, as an article, preposition, or conjunction, whether of a separate form class or not.
Roman Catholic Church. a small piece of the Host given to each lay communicant in a Eucharistic service.