1. slang Any psychotropic drug with potent hallucinogenic effects. My roommate in college was always on some kind of mind-bender or another. I heard someone slipped a mind-bender into his drink a couple hours ago, and he's been freaking out every since.

2. slang A puzzle that is especially challenging to solve, decipher, or understand. The game's puzzles are hardly mind-benders, but they'll get you thinking in creative ways. Her last riddle was a real mind-bender—it took me a few days to figure out!

3. slang Anything that challenges one's preconceived notions or the way one thinks about the world. The film is trying so hard to be a mind-bender with its twists and riddles that it forgets to be a well-made film in the process. Wow, what an interesting read—it was a real mind-bender!