1. 介词；前置词
A preposition is a word such as 'by', 'for', 'into', or 'with' which usually has a noun group as its object.

1. a function word that combines with a noun or pronoun or noun phrase to form a prepositional phrase that can have an adverbial or adjectival relation to some other word

2. (linguistics) the placing of one linguistic element before another (as placing a modifier before the word it modifies in a sentence or placing an affix before the base to which it is attached)