opacity

noun

opac·​i·​ty ō-ˈpa-sə-tē 

plural opacities

1

a

: 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)

Synonyms of opacity

• ambiguity
• ambiguousness
• mysteriousness
• opaqueness

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 including what the workers have discovered about their clients and deconstructing AI training systems from the inside out, Gourault challenges the opacity of automotive businesses that seek to conceal their association with extractive labor practices. —Farren Fei Yuan, Artforum, 1 Feb. 2026

What is different is the scale, the opacity and the fact that AI can turn yesterday’s seemingly harmless data into something far more revealing tomorrow. —Tony Bradley, Forbes.com, 26 Jan. 2026

Each shade’s opacity differs slightly, but most only require two coats (maximum of three). —Madison Yauger, PEOPLE, 22 Jan. 2026

Third parties are used for sampling water discharges and for opacity observations to ensure compliance with air and water regulations. —Maya Wilkins, Chicago Tribune, 21 Jan. 2026

Word History

Etymology

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

First Known Use

1575, in the meaning defined at sense 1a

Rhymes for opacity

• audacity
• capacity
• loquacity
• mendacity
• pugnacity
• rapacity
• sagacity
• tenacity
• veracity
• vivacity
• voracity
• incapacity

Kids Definition

opacity

noun

opac·​i·​ty ō-ˈpas-ət-ē 

plural opacities

: the quality or state of being opaque

Medical Definition

opacity

noun

opac·​i·​ty ō-ˈpas-ət-ē 

plural opacities

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)