root

The part of a plant, generally underground, that anchors and supports the plant body, absorbs and stores water and nutrients, and in some plants is able to perform vegetative reproduction.

A root vegetable.

The part of a tooth extending into the bone holding the tooth in place.

The part of a hair under the skin that holds the hair in place.

The part of a hair near the skin that has not been dyed, permed, or otherwise treated.

(figuratively) The primary source; origin.

(aviation) The section of a wing immediately adjacent to the fuselage.

(engineering) The bottom of the thread of a threaded object.

(arithmetic) Of a number or expression, a number which, when raised to a specified power, yields the specified number or expression.

(arithmetic) A square root (understood if no power is specified; in which case, "the root of" is often abbreviated to "root").

(mathematical analysis) A zero (of an equation).

(graph theory, computing) The single node of a tree that has no parent.

(linguistic morphology) The primary lexical unit of a word, which carries the most significant aspects of semantic content and cannot be reduced into smaller constituents. Inflectional stems often derive from roots.

(linguistics) A word from which another word or words are derived.

(music) The fundamental tone of any chord; the tone from whose harmonics, or overtones, a chord is composed.

The lowest place, position, or part.

(computing) In UNIX terminology, the first user account with complete access to the operating system and its configuration, found at the root of the directory structure; the person who manages accounts on a UNIX system.

(computing) The highest directory of a directory structure which may contain both files and subdirectories.

(slang) A penis, especially the base of a penis.