Radical a. : Of or pertaining to the root; proceeding directly from the root.

Radical a. : 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; as, radical evils; radical reform; a radical party.

Radical a. : Belonging to, or proceeding from, the root of a plant; as, radical tubers or hairs.

Radical a. : Proceeding from a rootlike stem, or one which does not rise above the ground; as, the radical leaves of the dandelion and the sidesaddle flower.

Radical a. : Relating, or belonging, to the root, or ultimate source of derivation; as, a radical verbal form.

Radical a. : Of or pertaining to a radix or root; as, a radical quantity; a radical sign. See below.

Radical n. : A primitive word; a radix, root, or simple, underived, uncompounded word; an etymon.

Radical n. : A primitive letter; a letter that belongs to the radix.

Radical n. : One who advocates radical changes in government or social institutions, especially such changes as are intended to level class inequalities; -- opposed to conservative.

Radical n. : A characteristic, essential, and fundamental constituent of any compound; hence, sometimes, an atom.

Radical n. : 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.

Radical n. : A radical quantity. See under Radical, a.

Radical a. : A radical vessel. See under Radical, a.

Example:
How many Radical friends and associations do you have?

Taxonomy
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Defination from the web:
Radical (chemistry) is an atom, molecule, or ion which is likely to take part in chemical reactions. The symbol used to indicate the square root or nth root ... Radical Republicans, a member of an influential group of American politicians during the Civil War reconstruction ...