radical (ˈrædɪkəl) adj.

1. Arising from or going to a root or source; basic: proposed a radical solution to the problem.

2. Departing markedly from the usual or customary; extreme or drastic: a radical change in diet.

3. Relating to or advocating fundamental or revolutionary changes in current practices, conditions, or institutions: radical politics; a radical political theorist.

4. Medicine Relating to or being surgery that is extreme or drastic in an effort to eradicate all existing or potential disease: radical hysterectomy.

5. Linguistics Of or being a root: a radical form.

6. Botany a. Of, relating to, or arising from a root: radical hairs. b. Arising from the base of a stem or from a below-ground stem or rhizome: radical leaves.

7. Slang Excellent; wonderful.