in·​jec·​tion | \ in-ˈjek-shən How to pronounce injection (audio) \

Definition of injection

1a : an act or instance of injecting
b : the placing of an artificial satellite or a spacecraft into an orbit or on a trajectory also : the time or place at which injection occurs
2 : something (such as a medication) that is injected
3 : a mathematical function that is a one-to-one mapping — compare bijection, surjection

Examples of injection in a Sentence

The medicine cannot be taken orally; it must be given by injection. an injection of a painkiller The struggling company needed an injection of cash.
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Recent Examples on the Web Some people have reported pain, redness and swelling around the injection site on their arms, or chills, fatigue and a headache, according to a U.S. Centers for Disease Control and Prevention web page on the Pfizer/BioNTech vaccine. David Anderson,, "Bel Air man who participated in trials of Pfizer’s COVID-19 vaccine says ‘no side effects,’ urges others to get their shot," 31 Dec. 2020 Other side effects can include a mild headache and pain and swelling at the injection site. Liz Hardaway,, "‘It feels like a big relief;’ San Antonio assisted living residents get first dose of coronavirus vaccine Tuesday," 29 Dec. 2020 In both Covid-19 trials, substantial majorities of participants in the vaccine group had local reactions at the injection site. Robert M. Kaplan And Dominick L. Frosch, WSJ, "Honesty Is the Best Policy in Selling Vaccines," 28 Dec. 2020 Dillaha said some people experience soreness at the injection site. Bill Bowden, Arkansas Online, "State sees smaller new-case increase," 28 Dec. 2020 In Moderna’s Phase 3 trials, the company said the most common side effects were fatigue, muscle soreness and aches, joint pain and headache, plus pain, redness or swelling at the injection site. Adrianna Rodriguez, USA TODAY, "There are two COVID-19 vaccines authorized in the US. Here's what we know about them.," 22 Dec. 2020 Some people also experience chills, a fever, and redness or swelling at the injection site. Sarah Jacoby, SELF, "Severe Allergic Reactions Are a Rare But Possible Side Effect of COVID-19 Vaccines," 22 Dec. 2020 Milder side effects, such as headaches, fatigue or pain at the injection site, are common and pass within a day or two, and are a sign that the vaccine is working to stimulate the immune system. Joel Achenbach, Anchorage Daily News, "US health authorities launch study on rare allergic reactions to coronavirus vaccine," 21 Dec. 2020 The most common side effects are injection site pain, fatigue, headache, muscle pain, and joint pain. Helen Branswell, STAT, "A side-by-side comparison of the Pfizer/BioNTech and Moderna vaccines," 19 Dec. 2020

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'injection.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of injection

15th century, in the meaning defined at sense 1a

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Time Traveler for injection

Time Traveler

The first known use of injection was in the 15th century

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Last Updated

15 Jan 2021

Cite this Entry

“Injection.” Dictionary, Merriam-Webster, Accessed 17 Jan. 2021.

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More Definitions for injection


How to pronounce injection (audio)

English Language Learners Definition of injection

: the act or process of forcing a liquid medicine or drug into someone or something by using a special needle
: the act or process of forcing a liquid into something
: the addition of something (such as money) that is needed to support something


in·​jec·​tion | \ in-ˈjek-shən How to pronounce injection (audio) \

Kids Definition of injection

: an act or instance of forcing a fluid (as a medicine) into a part of the body by using a special needle Insulin can be given by injection.


in·​jec·​tion | \ in-ˈjek-shən How to pronounce injection (audio) \

Medical Definition of injection

1a : the act or an instance of injecting a drug or other substance into the body
b : a solution (as of a drug) intended for injection (as by catheter or hypodermic syringe) either under or through the skin or into the tissues, a vein, or a body cavity
c : an act or process of injecting vessels or tissues also : a specimen prepared by injection
2 : the state of being injected : congestion — see circumcorneal injection

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