/op'euh ray"sheuhn/ , n.
1. an act or instance, process, or manner of functioning or operating.
2. the state of being operative (usually prec. by in or into ): a rule no longer in operation.
3. the power to act; efficacy, influence, or force.
4. the exertion of force, power, or influence; agency: the operation of alcohol on the mind.
5. a process of a practical or mechanical nature in some form of work or production: a delicate operation in watchmaking.
6. a course or procedure of productive or industrial activity: building operations.
7. a particular process or course: mental operations.
8. a business transaction, esp. one of a speculative nature; deal: a shady operation.
9. a business, esp. one run on a large scale: a multinational operation.
10. Surg. a procedure aimed at restoring or improving the health of a patient, as by correcting a malformation, removing diseased parts, implanting new parts, etc.
11. Math.
a. a mathematical process, as addition, multiplication, or differentiation.
b. the action of applying a mathematical process to a quantity or quantities.
12. Mil.
a. a campaign, mission, maneuver, or action.
b. Usually, operations . the conduct of a campaign, mission, etc.
c. operations , a headquarters, office, or place from which a military campaign, air traffic to and from an airfield, or any of various other activities, is planned, conducted, and controlled.
d. operations , the people who work at such a headquarters.
[ 1350-1400; ME operacioun operation- (s. of operatio ), equiv. to operat ( us ) (see OPERATE) + -ion- -ION ]