Opaque means you cannot see through it. Frosted bathroom glass, a china mug, a heavy curtain, milk in a glass: light stops or scatters, and the far side is simply gone.
English keeps three steps apart here, and it is worth learning them together: transparent is clear glass, translucent is a lampshade that passes light but no picture, opaque is a wall. Paint and ink are called opaque when they cover what is underneath in a single coat. The second life of the word is about understanding, and it is all over the news: opaque rules, opaque accounts, an opaque decision-making process, meaning nobody outside can see what is going on. That sense is an accusation, not a neutral description. The noun is opacity, and the verb opacify belongs to the laboratory.
1adjectivecolourImpossible to see through; letting no light pass.~76%
“The bottle was made of opaque brown glass.”
2adjectiveopaqueImpossible to understand, whether by accident or on purpose.~24%
“The contract was written in opaque legal language that nobody could follow.”
synonyms: impenetrable, obscure
Shares are an estimate: a language model read 17 sentences found in the wild and placed 17 of them on a sense — a count of our sample, not a measurement of English.
Opaque comes from Latin opacus, which meant shaded or shady, the dark under trees rather than a solid barrier. Middle English took it as opake, and Middle French opaque later pushed the spelling back towards the Latin. Where the Latin was about the shadow, English made the word about the thing blocking the light.
Latin
opacus — shaded, shady, dark
Middle English
opake
English, today
opaque
From Middle English opake, from Latin opacus (“shaded, shady, dark”) (of unknown origin), later reinforced from Middle French opaque. a doublet of ubac.
Etymology from Wiktionary, CC BY-SA