particle

noun6

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

   • Not every exasperated petty bourgeois could have become Hitler, but a particle of Hitler is lodged in every exasperated petty bourgeois. — 1933
2. •
   In the Roman Catholic church, a crumb of consecrated bread; also the smaller breads used in the communion of the laity.
3. •
   A little bit.

   • "That doesn't make a particle of difference", replied Charlotte. "Not a particle." — 1952
4. •
   Any of various physical objects making up the constituent parts of an atom; an elementary particle or subatomic particle.

   • What, he asked himself, does quantum theory have to say about the familiar properties of particles such as position? — 2011
5. •
   A part of speech that has no inherent lexical definition but must be associated with another word to impart meaning, often a grammatical category: for example, the English word to in a full infinitive phrase (to eat) or O in a vocative phrase (O Canada), or as a discourse marker (mmm).
6. •
   A part of speech which cannot be inflected.

   • 322. The parts of speech which are neither declined nor conjugated, are called by the general name of particles. 323. They are adverbs, prepositions, conjunctions, and interjections. — 1844