1. rude slang A stupid or silly person. A shortening of "feeble-minded," which can be considered offensive. Geez, he keeps pulling on a door that's clearly marked "push"—what a feeb.

2. slang An agent of the US Federal Bureau of Investigation. The term is formed from the first two letters of its initialism, "FBI." In this usage, the word is usually capitalized. Don't tell that guy anything—I think he's a Feeb.