- (mathematics) Relating to a radix or mathematical root.
"a radical quantity; a radical sign"
- Favoring fundamental change, or change at the root cause of a matter.
"His beliefs are radical."
"The spread of the cancer required radical surgery, and the entire organ was removed."
- (chemistry, not comparable) Involving free radicals.
- Pertaining to the basic or intrinsic nature of something.
- (linguistics, not comparable, of a sound) Produced using the root of the tongue.
- (slang, 1980s & 1990s) Excellent; awesome.
"That was a radical jump!"
- (botany, not comparable) Pertaining to a root (of a plant).
- (linguistics, not comparable) Of or pertaining to the root of a word.
- (historical: early 20th-century France) A member of an influential, centrist political party favouring moderate social reform, a republican constitution, and secular politics.
- (linguistics) 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.
- (organic chemistry) A free radical.
- (historical: 19th-century Britain) A member of the most progressive wing of the Liberal Party; someone favouring social reform (but generally stopping short of socialism).
- (arithmetic) A root (of a number or quantity).
- (chemistry) A group of atoms, joined by covalent bonds, that take part in reactions as a single unit.
- A person with radical opinions.
- (linguistics) In Semitic languages, any one of the set of consonants (typically three) that make up a root.