opac·​i·​ty | \ō-ˈpa-sə-tē \
plural opacities

Definition of opacity 

1a : obscurity of sense : unintelligibility

b : the quality or state of being mentally obtuse : dullness

2 : the quality or state of a body that makes it impervious to the rays of light broadly : the relative capacity of matter to obstruct the transmission of radiant energy

3 : an opaque spot in a normally transparent structure (such as the lens of the eye)

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Examples of opacity in a Sentence

the opacity of the glass Critics have noted the opacity of her writing style.

Recent Examples on the Web

By June 2, Opportunity could see notable effects of the storm in the sky as the atmospheric opacity, or tau level, increased from 0.6 (a typical day on Mars) to 2. Jay Bennett, Popular Mechanics, "NASA Optimistic That Opportunity Can Survive Martian Dust Storm," 13 June 2018 Their past opacity has shielded them from searching criticism, but exposed them instead to the laziest disdain. The Economist, "China’s statistics are bad. Many criticisms of them are worse," 7 July 2018 Tether, another virtual currency that has attempted to tie tokens to U.S. dollars, has faced criticism for its opacity. Robert Hackett, Fortune, "Cryptocurrency Exchange Circle Valued at Nearly $3 Billion After Poloniex Deal," 15 May 2018 Such opacity has presented an opportunity for Coinbase, which has both an easy-to-use mobile app and a law-abiding reputation. The Economist, "A disciplined startup emerges from the Wild West of crypto-currency," 28 June 2018 Though journalists have long criticized the EPA under Obama and George W. Bush for a lack of transparency, Pruitt's tenure was marked by an unprecedented opacity. Dino Grandoni, Washington Post, "The Energy 202: The EPA won't change policy after Pruitt. But it might be more transparent about it.," 10 July 2018 Forster captures the complexity of Indian society with its vying religions and languages, creating an opacity frustrating to the British Raj. John Timpane, Philly.com, "'Passage' at the Wilma Theater: E.M. Forster must be turning in his grave," 26 Apr. 2018 Each book ends up a meditation on the opacity of class experience, to those who live in it but also to those who theorize it. Jedediah Purdy, The New Republic, "The Remaking of Class," 27 June 2018 Romantic love doesn’t lessen the opacity of other people’s thoughts and motivations. refinery29.com, "Read This & You’ll Never Hear “...Baby One More Time” The Same Way Again," 26 June 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'opacity.' 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 opacity

1575, in the meaning defined at sense 1a

History and Etymology for opacity

Middle French opacité shadiness, from Latin opacitat-, opacitas, from opacus shaded, dark

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Statistics for opacity

Last Updated

9 Nov 2018

Look-up Popularity

Time Traveler for opacity

The first known use of opacity was in 1575

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More Definitions for opacity



English Language Learners Definition of opacity

: the quality of a material that does not allow light to pass through it : the quality of being opaque

: the quality of being difficult to understand or explain


opac·​i·​ty | \ō-ˈpas-ət-ē \
plural opacities

Medical Definition of opacity 

1 : the quality or state of a body that makes it impervious to the rays of light broadly : the relative capacity of matter to obstruct by absorption or reflection the transmission of radiant energy (as X-rays, infrared radiation, or sound)

2 : an opaque spot in a normally transparent structure (as the lens of the eye)

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Comments on opacity

What made you want to look up opacity? Please tell us where you read or heard it (including the quote, if possible).


something that serves to warn or remind

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