In mathematics, a radical is the symbol used to indicate the square (or cube, or other) root operation. In chemistry, a radical (sometimes called a “free radical”) is an atom, ion, or molecule that has an unpaired valence electron, and thus is highly reactive. In politics, a radical is one who subscribes to extremist viewpoints. In youth culture, something radical is just far out, dude. Except their way to hip to go to the trouble of pronouncing all those syllables, so radical is just “rad.”