operation
noun
ˌɒpəˈreɪʃn 
ˌɑːpəˈreɪʃn medical
1 (also British English informal op) [countable] the process of cutting open a part of a person's body in order to remove or repair a damaged partWill I need to have an operation?He underwent a three-hour heart operation.operation (on somebody/something) (to do something) an operation on her lung to remove a tumouroperation (on somebody/something) (for something) Doctors performed an emergency operation for appendicitis last night.organized activity
2 [countable] an organized activity that involves several people doing different thingsa security operationThe police have launched a major operation against drug suppliers.the UN peacekeeping operationsbusiness
3 [countable, usually plural] a business or company involving many partsa huge multinational operation4 [countable] the activity or work done in an area of business or industrythe firm's banking operations overseascomputer
5 [countable, uncountable] an act performed by a machine, especially a computerThe whole operation is performed in less than three seconds.machine/system
6 [uncountable] the way that parts of a machine or a system work; the process of making something workRegular servicing guarantees the smooth operation of the engine.Operation of the device is extremely simple.military activity
7 [countable, usually plural] military activityHe was the officer in charge of operations.mathematics
8 [countable] a process in which a number or quantity is changed by adding, multiplying, etc.Idioms
in operation
working, being used or having an effect
The system has been in operation for six months.Temporary traffic controls are in operation on New Road.come into operation
to start working; to start having an effect
Synonym
come into forceThe new rules come into operation from next week.put something into operation
to make something start working; to start using something
It's time to put our plan into operation.
Usage note: IllnessesBecoming illcatch a cold/an infectious disease/the flu/(British English) flu/pneumonia/a virus/(informal) a bugget (British English) ill/(North American English) sick/a disease/AIDS/breast cancer/a cold/the flu/(British English) flu/a migrainecome down with a cold/the flu/(British English) flucontract a deadly disease/a serious illness/HIV/AIDSbe infected with a virus/a parasite/HIVdevelop cancer/diabetes/a rash/an ulcer/symptoms of hepatitishave a heart attack/a strokeprovoke/trigger/produce an allergic reactionblock/burst/rupture a blood vesseldamage/sever a nerve/an artery/a tendonBeing illfeel (British English) ill/sick/nauseous/queasybe running (British English) a temperature/(North American English) a feverhave a head cold/diabetes/heart disease/lung cancer/a headache/(British English) a high temperature/(North American English) a feversuffer from asthma/malnutrition/frequent headaches/bouts of depression/a mental disorderbe laid up with/(British English) be in bed with a cold/the flu/(British English) flu/a migrainenurse a cold/a headache/a hangoverbattle/fight cancer/depression/addiction/alcoholismTreatmentsexamine a patientdiagnose a condition/disease/disorderbe diagnosed with cancer/diabetes/schizophreniaprescribe/be given/be on/take drugs/medicine/medication/pills/painkillers/antibioticstreat somebody for cancer/depression/shockhave/undergo an examination/an operation/surgery/a kidney transplant/therapy/chemotherapy/treatment for cancerhave/be given an injection/(British English) a flu jab/(North American English) a flu shot/a blood transfusion/a scan/an X-raycure a disease/an ailment/cancer/a headache/a patientprevent the spread of disease/further outbreaks/damage to the lungsbe vaccinated against the flu/(British English) flu/the measles/(British English) measles/polio/smallpoxenhance/boost/confer/build immunity to a disease