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: radical opinions on education.
3. favoring or effecting fundamental or revolutionary changes in current practices, conditions, or institutions: radical political views.
4. linguistics of or being a root: a radical form.
5. botany arising from the root or its crown: radical leaves.
6. slang excellent; wonderful.
7. one who advocates fundamental or revolutionary changes in current practices, conditions, or institutions: radicals seeking to overthrow the social order.
8. mathematics the root of a quantity as indicated by the radical sign.
9. an atom or a group of atoms with at least one unpaired electron.
10. linguistics see root1.

1. favouring fundamental change, or change at the root cause of a matter.
2. of or pertaining to a root (of a plant).
3. of or pertaining to the intrinsic nature of something.
4. thoroughgoing.
5. of or pertaining to the root of a word.
6. involving free radicals
7. excellent.
8. A member of the most progressive wing of the liberal party; someone favouring social reform (but generally stopping short of socialism).
9. A member of an influential, centrist political party favouring moderate social reform, a republican constitution, and secular politics.
10. A person with radical opinions.
11. A root (of a number or quantity).
12. in logographic writing systems as the chinese writing system, the portion of a character (if any) that provides an indication of its meaning, as opposed to phonetic.
13. in semitic languages, any one of the set of consonants (typically three) that make up a root.
14. A group of atoms, joined by covalent bonds, that take part in reactions as a single unit.
15. A free radical.

1. of or pertaining to the root; proceeding directly from the root.
2. hence: of or pertaining to the root or origin; reaching to the center, to the foundation, to the ultimate sources, to the principles, or the like; original; fundamental; thorough-going; unsparing; extreme
3.
4. belonging to, or proceeding from, the root of a plant.
5. proceeding from a rootlike stem, or one which does not rise above the ground.
6. relating, or belonging, to the root, or ultimate source of derivation.
7. of or pertaining to a radix or root
8.
9. A primitive word; a radix, root, or simple, underived, uncompounded word; an etymon.
10. A primitive letter; a letter that belongs to the radix.
11. one who advocates radical changes in government or social institutions, especially such changes as are intended to level class inequalities; -- opposed to conservative.
12.
13. A characteristic, essential, and fundamental constituent of any compound; hence, sometimes, an atom.
14. specifically, a group of two or more atoms, not completely saturated, which are so linked that their union implies certain properties, and are conveniently regarded as playing the part of a single atom; a residue; -- called also a compound radical. cf. residue.
15. A radical quantity. see under radical, a.
16. A radical vessel. see under radical, a.

1. pertaining or relating to a root or to roots.
2. specifically— in botany, belonging to the root: opposed to cauline. see radical leaves and radical peduncle, below.
3. in philology, of the nature of or pertaining to a root, or a primary or underived word or main part of a word: as, a radical word; a radical letter or syllable; radical accentuation.
4. in mathematics, consisting of or indicating one of the roots of a number: as, a radical expression; the radical sign.
5. in chem., noting any atom or group of atoms which is, for the moment, regarded as a chief constituent of the molecules of a given compound, and which does not lose its integrity in the ordinary chemical reactions to which the substance is liable.
6. making part of the essential nature of the subject or thing concerned; existing inherently; intrinsic; organic: as, radical defects of character; a radical fault of construction; the radical principles of an art or of religion.
7. of or pertaining to the root or foundation of the subject; concerned with or based upon fundamental principles; hence, thoroughgoing; extreme: as, a radical truth; a radical difference of opinion; radical views or measures; the radical party in british politics.
8. of or pertaining to a political party or body of persons known as radicals (see II., 4, below): as, a radical candidate; the radical program.
9.
10. in philology:
11. A radical word or part of a word; especially, a primitive word or verbal element serving as a root of inflected or derivative words.
12. A radical letter; a letter forming an essential part of the primitive form or root of a word. also radicle.
13. in chem., an element or group of combined elements which remains after one or more elements have been removed from a compound. (see the quotation.)
14. in music, same as root.
15. A person who holds or acts according to radical principles; one who pursues a theory to its furthest apparent limit; an extremist, especially in politics.
16. in algebra, a quantity expressed as a root of another quantity.
17. see the adjectives.
18. in astrology, belonging to the radix or original scheme of nativity; in horary astrology, ripe and proper for judgment.
19. A minute vessel which unites with others to form a large branch or trunk. see radicle, 2.
20. in england, the name given to a white hat which was formerly somewhat worn by radicals, owing to the fact that henry hunt [a radical english politician, 1773–1835] wore a white hat at various political gatherings in 1820.

1. (chemistry) two or more atoms bound together as a single unit and forming part of a molecule
2. (linguistics) the form of a word after all affixes are removed
3. 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. (mathematics) a quantity expressed as the root of another quantity
5. of or relating to or constituting a linguistic root
6. arising from or going to the root or source
7. a character conveying the lexical meaning of a logogram
8. (used of opinions and actions) far beyond the norm
9. a person who has radical ideas or opinions
10. markedly new or introducing radical change
11. 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