WordNet sense 1 (an atom or group of atoms with at least one unpaired electron; in the body it is usually an oxygen molecule than has lost an electron and will stabilize itself by stealing an electron from a nearby molecule):

free radical

WordNet sense 2 ((chemistry) two or more atoms bound together as a single unit and forming part of a molecule):

group, chemical group

WordNet sense 3 (a sign placed in front of an expression to denote that a root is to be extracted):

radical sign

WordNet sense 4 ((linguistics) the form of a word after all affixes are removed):

base, root, stem, theme, root word

WordNet sense 5 (markedly new or introducing radical change):

revolutionary

WordNet sense 6 (not of long duration; having just (or relatively recently) come into being or been made or acquired or discovered):

new

WordNet sense 7 ((used of opinions and actions) far beyond the norm):

extremist, ultra

WordNet sense 8 (not within reasonable limits):

immoderate

WordNet sense 9 (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):

basal