sector

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A part or division, as of a city or a national economy.
• noun The portion of a circle bounded by two radii and the included arc.
• noun A measuring instrument consisting of two graduated arms hinged together at one end.
• noun Computers A portion of a magnetic storage device making up the smallest addressable unit of information.
• noun A division of a defensive position for which one military unit is responsible.
• noun A division of an offensive military position.
• transitive verb To divide (something) into sectors.

from The Century Dictionary.

• noun A cutting implement or device.
• noun In geometry:
• noun A plane figure inclosed between the arc of a circle, ellipse, or other central curve and two radii to its extremities from the center. Thus, in the figure, CDB is a sector of a circle.
• noun A solid generated by the revolution of a plane sector about one of its radii.
• noun A mathematical rule consisting of two flat pieces connected by a stiff rule-joint so that the broad sides move in their own planes, and bearing various scales, especially double scales which are scales of trigonometric functions, etc., duplicated on the two pieces and radiating from the center of the joint.
• noun An astronomical instrument consisting of a telescope turning about the center of a graduated arc. It was formerly used for measuring differences of declination. See zenith-sector.
• noun In mech., a toothed gear of which the face is an arc of a circle, intended for reciprocating action. See cut under operating-table.
• noun In entomology, one of the veins of the wing of some insects, as the ephemerids; a branch of the cubitus.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Geom.) A part of a circle comprehended between two radii and the included arc.
• noun A mathematical instrument, consisting of two rulers connected at one end by a joint, each arm marked with several scales, as of equal parts, chords, sines, tangents, etc., one scale of each kind on each arm, and all on lines radiating from the common center of motion. The sector is used for plotting, etc., to any scale.
• noun An astronomical instrument, the limb of which embraces a small portion only of a circle, used for measuring differences of declination too great for the compass of a micrometer. When it is used for measuring zenith distances of stars, it is called a zenith sector.
• noun an instrument used for measuring the dip of the horizon.
• noun the solid generated by the revolution of the sector of a circle about one of its radii, or, more rarely, about any straight line drawn in the plane of the sector through its vertex.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun section
• noun zone (designated area)
• noun geometry A part of a circle, extending to the center.
• noun computing a fixed-sized unit (traditionally 512 bytes) of sequential data stored on a track of a digital medium (compare to block)
• noun military An area designated by boundaries within which a unit operates, and for which it is responsible.
• noun military One of the subdivisions of a coastal frontier.
• noun science fiction a fictional region of space designated for navigational or governance purposes; for instance, W:Sector (Star Trek), W:List of Star Wars sectors

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a particular aspect of life or activity
• noun measuring instrument consisting of two graduated arms hinged at one end
• noun a plane figure bounded by two radii and the included arc of a circle
• noun the minimum track length that can be assigned to store information; unless otherwise specified a sector of data consists of 512 bytes
• noun a portion of a military position
• noun a social group that forms part of the society or the economy