1.Definition: (used of opinions and actions) far beyond the norm
"Radical opinions on education"
2.Definition: arising from or going to the root or source
"A radical flaw in the plan"
3.Definition: especially of leaves; located at the base of a plant or stem; especially arising directly from the root or rootstock or a root-like stem
4.Definition: markedly new or introducing radical change
"Radical political views"
5.Definition: of or relating to or constituting a linguistic root
"A radical verb form"