radical radical /ˈrædɪkəl/

adjective

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

noun

1. () (chemistry) two or more atoms bound together as a single unit and forming part of a molecule  ( chemical group , group , radical )
   (chemistry) two or more atoms bound together as a single unit and forming part of a molecule
   
2. () 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  ( free radical , radical )
   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
   in the body free radicals are high-energy particles that ricochet wildly and damage cells
   
3. () A person who has radical ideas or opinions  ( radical )
   a person who has radical ideas or opinions
   
4. (linguistics) the form of a word after all affixes are removed  ( base , radical , root word , root , stem , theme )
   (linguistics) the form of a word after all affixes are removed
    Thematic vowels are part of the stem
   thematic vowels are part of the stem
   
5. A character conveying the lexical meaning of a logogram  ( radical )
   a character conveying the lexical meaning of a logogram
   
6. (mathematics) a quantity expressed as the root of another quantity  ( radical )
   (mathematics) a quantity expressed as the root of another quantity