n. part of speech that serves to express the relationship between two words (Grammar)
n. preposition, part of speech that serves to express the relationship between two words (Grammar)
1. Any of a closed class of non-inflecting words typically employed to connect a following noun or a pronoun, in an adjectival or adverbial sense, with some other word: a particle used with a noun or pronoun (in English always in the objective case) to make a phrase limiting some other word.