a (context|linguistics|not comparable) Of or pertaining to the root of a word.
a (context|chemistry|not comparable) Involving free radicals
a (slang|1990s) Excellent.
n (context|historical: 19th-century England) A member of the most progressive wing of the Liberal Party; someone favouring social reform (but generally stopping short of socialism).
n (context|historical: early 20th-century France) A member of an influential, centrist political party favouring moderate social reform, a republican constitution, and secular politics.
n A person with radical opinions.
n (context|arithmetic) A root (of a number or quantity).
n (context|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'.
n (context|linguistics) In Semitic languages, any one of the set of consonants (typically three) that make up a root.