- any member of a class of words found in many languages that are used before nouns, pronouns, or other substantives to form phrases functioning as modifiers of verbs, nouns, or adjectives, and that typically express a spatial, temporal, or other relationship, as in, on, by, to, since.
- to position in advance or beforehand: to preposition troops in anticipated trouble spots.
- a word or group of words used before a noun or pronoun to relate it grammatically or semantically to some other constituent of a sentence
