radical in WordNet English dictionary

1. 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 placentation"; "radical leaves"
   radical  basal 
   
2. (used of opinions and actions) far beyond the norm
   "extremist political views"; "radical opinions on education"; "an ultra conservative"
   extremist  radical  ultra 
   
3. of or relating to or constituting a linguistic root
   "a radical verb form"
   radical 
   
4. arising from or going to the root or source
   "a radical flaw in the plan"
   radical 
   
5. markedly new or introducing radical change
   "a revolutionary discovery"; "radical political views"
   revolutionary  radical 
   

1. (linguistics) the form of a word after all affixes are removed
   "thematic vowels are part of the stem"
   root  root word  base  stem  theme  radical 
   
2. (chemistry) two or more atoms bound together as a single unit and forming part of a molecule
   group  radical  chemical group 
   
3. an atom or group of atoms with at least one unpaired electron; in the body it is usually an oxygen molecule that has lost an electron and will stabilize itself by stealing an electron from a nearby molecule
   "in the body free radicals are high-energy particles that ricochet wildly and damage cells"
   free radical  radical 
   
4. a character conveying the lexical meaning of a logogram
   radical 
   
5. a person who has radical ideas or opinions
   radical 
   
6. (mathematics) a quantity expressed as the root of another quantity
   radical