(Latin: not transparent nor translucent, not clear, unable to shine through; shaded, shady; dark; no luster; not clearly understood or expressed)

electron opaque tracer, electron-opaque tracer (s) (noun), electron opaque tracers, electron-opaque tracers (pl)
A metallic salt often found in association with binding proteins; such as, antibodies: An electron-opaque tracer is used to detect the presence of specific molecules or structures in an electron microscopic examination of a sample.
Isopaque (s) (noun), Isopaques (pl)
A medical contrast medium, or contrast agent, that is a trademark which is used for the preparation of a diagnostic radiopaque medium: An Isopaque is a substance used to enhance the variations of structures or fluids within the body during medical X-ray imaging.

The Isopaque is commonly used to show the differences between the visibility of blood vessels and the gastrointestinal tract in the body.

nonopaque (adjective), more nonopaque, most nonopaque
1. A reference to physically allowing the passage of radiation, or X-rays, to go through objects: The nonopaque radiation procedures make it possible for X-rays to be radiolucent or to allow the passage of radiant energy to go through materials so they are not blocking the process.
2. Not being difficult to understand; and so, being clear and obvious: The nonopaque language of the scientist made it possible for the non-scientific audience to understand what he was talking about.
opacity (s) (noun), opacities (pl)
1. A thick or dark condition that makes something; such as, glass or a liquid difficult to see through: The opacity of Shareen's windows were a result of not having the accumulation of dirt cleaned off.

Opacities represent the degrees to which light is obscured by pollutant particles in the air.

2. Having difficulty in understanding statements, presentations, or in explaining something: Students had difficulty in understanding the opacity of the teacher's scientific presentation.

The opacities of most dictionaries simply don't give people clear or straightforward definitions.

3. Etymology: "darkness, obscurity", from French opacité; from Latin opacitatem, opacitas, "shade, shadiness"; from opacus, "shaded, dark".
opaque (adjective), opaquer, opaquest
1. A reference to not being clear; not transmitting radiant energy, sound, heat, etc.: Opaque elements are characterized by being opposite to that of transparency; for example, steel is an opaque material that blocks visible light.

Certain chemical solutions are opaque to ultraviolet radiations.

There was a dust cloud of opaque pollution over Karen's city that was caused by the dust storm.

2. Relating to something that is not clearly understood or expressed; not clear or lucid; obscure: Medical dictionaries too often provide the most opaque definitions of any of the other lexicons.

Despite the professor's help, the scientific presentation still seems opaque for some of his students.

3. Characteristic of impervious to light; not translucent or only slightly so: The winter opaque glass blocked any possibility of looking outside Adam's windows.
4. Descriptive of not allowing light to pass through: The opaque water of the muddy river made it impossible to see anything below the surface of the water.
5. Referring to not shining, without luster, not reflecting light; or being dark or dull: The opaque paint on Kate's car would not reflect the glare from the sun even on very sunny days.
6. Pertaining to dull, stupid, or unintelligent conversations: Some of the most opaque remarks are presented by certain radio talk-show hosts.

It's amazing how some politicians can pass such opaque bills that waste so much federal money.

7. Etymology: from opake which came from Latin opacus, "dark, shaded, shady" of uncertain origin. The current English spelling of opaque was influenced from about 1650 by French opaque which came from Latin.
opaque projector (s) (noun), opaque projectors (pl)
A medium that does not pass radiation of a particular frequency band: Opaque projectors are used to view images of nontransparent materials; such as, printed sheets, pages of books, drawings, mineral specimens, leaves, etc. onto a screen by means of reflected light for lectures and presentations.
opaque, translucent, transparent
opaque (oh PAYK) (adjective)
1. Difficult to understand: Manfred's oral instructions were opaque and Dennis had to ask for an explanation.
2. Regarding something which does not allow light to pass through: The windows were painted black so they would be opaque, thus permitting the photographer to work in his photo-processing laboratory without unwanted illumination.
translucent (trans LOO suhnt, tranz LOO suhnt) (adjective)
Pertaining to something which is not completely clear or transparent, but clear enough to allow light to pass through: The frosted glass in the door was translucent.
transparent (trans PAIR uhnt, trans PAHR uhnt) (adjective)
1. Concerning light being able to pass through: The new window in the sunroom was transparent and let in all the sunshine.
2. Characteristic of something self-evident; obvious; apparent: Trina's facial expression was so transparent that Susan always knew what she was thinking.

The information from the lecture was completely opaque to Ryan and so he couldn't understand a thing.

After Howard read the text book, his mind felt more translucent, as if some light on the subject was getting through and the information was beginning to make sense, but not completely.

Then, after Marla asked for an explanation, the answer suddenly became transparent.

opaquely (adverb), more opaquely, most opaquely
Relating to being unable to see through something which is not transparent: The opaquely steamed windows that Jane has will always prevent anyone from being able to see through them.
opaqueness (s) (noun), opaquenesses (pl)
1. The quality or the degree to which something reduces the passage of light: The opaqueness of the dirty windows permitted little light to pass through them and so they were not translucent or they were just clear enough for light to pass through them, but only with difficulty.

Dust storms are common across Arizona during dry and windy conditions, and walls of dust more than a mile high can blanket an area in a matter of seconds, sometimes reducing visibility to zero or complete opaqueness.

2. Incomprehensibility resulting from the obscurity or difficulty of understanding someone or something: The opaqueness of technical jargon found in most scientific dictionaries makes it very difficult for the average user to understand what is being presented.

Why must so many medical lexicons have such opaquenesses in their content?

radiopaque (adjective), more radiopaque, most radiopaque
Descriptive of not allowing the passage of radiation; especially X-rays, gamma rays, or other forms of radiant energy to be used: In diagnostic X-ray imaging, it is sometimes necessary to introduce special radiopague dyes into the body to make the organs stand out more clearly.

During the procedure for obtaining X-ray pictures of the urinary system, or urography, the technique involves the introduction of a radiopaque, iodine-based dye into the kidneys, ureters, and bladder so they will show up better on X-rays.

roentgenopaque, röntgenopaque (s) (adjectives), more roentgenopaque, röntgenopaque, most roentgenopaque, röntgenopaque
Relating to not permitting the passage or transmission of x-rays: Roentgenopaque or radiopaque X-rays are impenetrable to certain materials and so an image is produced on a radiosensitive surface; such as, photographic film, by radiation other than with visible light.

There are roentgenopaque materials that are not penetrable by roentgen rays at the commonly used diagnostic energy procedures. Such roentgenopaque areas appear light or white on exposed films.

semiopaque (adjective) (not comparable)
A reference to partially or nearly half transmitting or reflecting of light or radiant energy: Many of the new buildings in Sam's city have semiopaque windows.

Some semiopaque glazes are applied to ceramics before firing so they will have a smooth lustrous surfaces and be more attractive.