omicron

noun

om·​i·​cron ˈō-mə-ˌkrän  ˈä-mə-ˌkrän 

 British also  ō-ˈmī-(ˌ)krän

plural omicrons

1

: the 15th letter of the Greek alphabet see Alphabet Table

2

or less commonly Omicron : omicron variant

The speed of omicron's rise is quicker than the rise of previous variants of the virus, said Hannah Barbian, a Rush University Medical Center virologist who worked on the testing.

—Sarah Freishtat

How a Virus Got Its Name: Usage Guide

In November 2021, a COVID-19 variant was named Omicron, after the 15th letter of the Greek alphabet. The World Health Organization uses Greek letters to name variants, because these names are easier to communicate than scientific designations like B.1.617.2. According to the WHO, the 13th and 14th Greek letters (nu and xi) were skipped over because "nu" sounds like "new," and "xi" is also a common surname.

How to Pronounce Omicron: Usage Guide

The pronunciation of omicron has several variant forms acceptable in standard English. In American English, the primary stress is usually on the first syllable, pronounced as either a short \o\ as \ˈä-mə-ˌkrän\ or a long \o\ as \ˈō-mə-ˌkrän\. In British English, the primary stress can also be heard on the second syllable: \ō-ˈmī-(ˌ)krän\.

Examples of omicron in a Sentence

Recent Examples on the Web

Last fall’s recipe was tailored to omicron descendants on the JN.1 branch of the virus family tree. —Lauran Neergaard, Chicago Tribune, 22 May 2025

For comparison, on Jan 17, 2022, during the Covid omicron surge, 278 people were boarded. —Erika Edwards, NBC News, 7 Feb. 2024

This is a switch from the current formula, which is bivalent, targeting both the spike protein from the ancestral SARS-CoV-2 strain and the previous leading omicron subvariants BA.4/5 (which share a spike protein). —Beth Mole, Ars Technica, 15 June 2023

Most of the children with RSV and omicron were younger than 2 years of age (77.7% and 72.3%, respectively) while 81% of children with the flu were older. —Katherine Kahn | Medpage Today, ABC News, 27 Dec. 2023

Word History

Etymology

Middle English, from Greek o mikron, literally, small o

First Known Use

1631, in the meaning defined at sense 1

Phrases Containing omicron

• omicron variant

Rhymes for omicron

• aileron
• antiphon
• autobahn
• carillon
• castellan
• celadon
• cephalon
• chitosan
• cynodon
• denouement
• deuteron
• echelon

Kids Definition

omicron

noun

omi·​cron

ˈäm-ə-ˌkrän,

ˈōm-

: the 15th letter of the Greek alphabet

—Ο or ο

Etymology

from Greek o mikron, literally, "small o"

Medical Definition

omicron

noun

om·​i·​cron ˈō-mə-ˌkrän  ˈä-mə-ˌkrän 

 British also  ō-ˈmī-(ˌ)krän

1

: the 15th letter of the Greek alphabet

2

also Omicron : omicron variant

After the emergence of omicron was announced, several nations imposed travel bans hoping to contain the virus.

—Louis Jacobson, California Healthline

The CDC said that data show COVID-19 boosters help boost protection against Omicron and other SARS-CoV-2 variants.

—FDAnews Drug Daily Bulletin