Emily Dickinson Lexicon

RAD'IC-AL, n.

1. In philology, a primitive word; a radix, root, or simple underived uncompounded word.
2. A primitive letter; a letter that belongs to the radix.
3. In modern politics, a person who advocates a radical reform, or extreme measures in reformation.
4. In chimistry, an element, or a simple constituent part of a substance, which is incapable of decomposition. – Parke. That which constitutes the distinguishing part of an acid or a base, by its union with oxygen, or other acidifying and basifying principles. – Ure. Compound radical, is a base composed of two or more substances. Thus a vegetable acid having a radical composed of hydrogen and carbon, is said to be an acid with a compound radical. Radical quantities, in algebra, quantities whose roots may be accurately expressed in numbers. The term is sometimes extended to all quantities under the radical sign. Radical sign, the sign √ placed before any quantity, denoting that its root is to be extracted; thus, √a or √(a+b). – Encyc. Bailey.