1. To move or travel below, beneath, or underneath someone or something. I find a sort of melancholy joy watching people pass under my window at work. The people on the bridge cheered as the kayakers passed under them.

2. To deliver something to someone by surreptitiously handing it to them underneath something. In this usage, one or two nouns or pronouns are used between "pass" and "under" to specify what is being passed and, in some cases, the person receiving it. Teacher! Tommy's passing notes under the desks! Quick, pass me your comic book under the table so the teacher doesn't see it!