The phrase "rent air" is typically used to describe a situation where one is speaking or making noise without actually conveying any meaningful information. There are a number of synonyms for this term, including "babble," "prattle," "chatter," "drone," and "ramble." Other related terms might include "jabber," "yammer," "mumble," and "gibber." These words all share the sense of making a lot of noise but not really saying anything of substance. In many cases, "rent air" occurs when someone is nervous or unsure of what to say, and ends up filling the silence with meaningless words.