adj

• (botany, not comparable) Pertaining to a root (of a plant).
• (lexicography, not comparable) Of or pertaining to the root of a word.
• (phonology, phonetics, not comparable, of a sound) Produced using the root of the tongue.
• (chemistry, not comparable) Involving free radicals.

noun

• (historical, 19th-century Britain, politics) A member of the most progressive wing of the Liberal Party; someone favouring social reform (but generally stopping short of socialism).
• (historical, early 20th-century France) A member of an influential, centrist political party favouring moderate social reform, a republican constitution, and secular politics.
• (arithmetic) A root (of a number or quantity).
• (linguistics) In logographic writing systems such as the Chinese writing system, the portion of a character (if any) that provides an indication of its meaning, as opposed to phonetic.
  "The boy recognised the Chinese characters, though the calligraphy looked a bit strange, as if drawn by someone who had seen them and copied them out radical by radical without knowing what they meant."