/ ˈsektə(r); NAmE / noun
1.
a part of an area of activity, especially of a country's economy :
the manufacturing sector
service-sector jobs (= in hotels, restaurants, etc.)
—see also the private sector , the public sector
2.
a part of a particular area, especially an area under military control :
each sector of the war zone
3.
( geometry ) a part of a circle lying between two straight lines drawn from the centre to the edge
—picture at circle
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WORD ORIGIN
late 16th cent. (in sense 3): from late Latin , a technical use of Latin sector cutter, from sect- cut off, from the verb secare .