Definify.com
Webster 1913 Edition
Sector
1.
(Geom.)
A part of a circle comprehended between two radii and the included arc.
2.
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.
3.
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.
Dip sector
, an instrument used for measuring the dip of the horizon.
– Sector of a sphere
, or Spherical sector
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.
Webster 1828 Edition
Sector
SECT'OR
,Noun.
1. In geometry, a part of a circle comprehended between two radii and the arch; or a mixed triangle, formed by two radii and the arch of a circle.
2. A mathematical instrument so marked with lines of sines, tangents, secants, chords, &c. as to fit all radii and scales, and useful in finding the proportion between quantities of the same kind. The sector is founded on the fourth proposition of the sixth book of Euclid, where it is proved that similar triangles have their homologous sides proportional.