1. To stand in a row directly behind someone or something else. I had to line up behind some guy with terrible body odor. Make sure that each book is lined up behind the previous entry in the series.

2. To cause or direct someone or something to form or get into a row directly behind someone or something else. In this usage, a noun or pronoun can be used before or after "up." The teacher lined me up behind Jeremy because I'm a little bit taller than him I've been lining up my DVDs behind my collection of VHS tapes.

3. To stand in a row behind some larger thing, such as a building. We have to line up behind the courthouse every morning to report for our community service. The actors are lined up behind the curtain, waiting for their cues.

4. To cause or direct someone or something to stand in a row behind some larger thing. In this usage, a noun or pronoun can be used before or after "up." Line the students up behind the gymnasium and we'll divide them into two teams for a soccer game. He lined up his collection of figurines behind a bookshelf in his room.

5. To stand in solidarity with or support of someone or something. We all lined up behind our friend Tom when he announced he would be running for Mayor. To their credit, everyone at the company lined up behind me when the accusations came to light.

6. To organize people in solidarity with or support of a person, group, or organization. In this usage, a noun or pronoun can be used before or after "up." A number of high-profile campaign groups have spent a lot of time and money trying to line people up behind the incumbent president. The principal has been lining teachers up behind their colleague in her fight against cancer.