a word employed to connect a 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; -- so called because usually placed before the word with which it is phrased; as, a bridge of iron; he comes from town; it is good for food; he escaped by running.-a proposition; an exposition; a discourse.