Radiopaque

Part of speech: adjective

Definitions

1. Characterizing materials that obstruct radiation, resulting in them appearing prominently in radiological images
2. Describing substances that hinder the transmission of radiation, making them visible as lighter areas on diagnostic scans
3. Referring to substances that block radiation, thereby making them appear as distinct light spots in imaging studies

Etymology: "Radiopaque" is a plain technical coinage from the early twentieth century, and its first recorded use dates to 1917. It joins "radi-", a combining form from Latin "radius" meaning "staff" or "ray", with "opaque", which English took from Latin "opacus" ("shaded, dark") by way of Middle English and Middle French. Together they describe something that blocks X-rays, which were themselves only discovered in 1895, so the word was built almost as soon as the phenomenon it names came into view. The combining form "radi-" is the same one that appears in "radiology" and "radiation", and it carries the sense of rays rather than the Latin "radius" in its geometric sense. Medicine needed a precise way to say that a substance would show up as a shadow on a photographic plate, and "radiopaque" supplied that. Its partner, "radiolucent", describes the opposite: material that X-rays pass through, leaving no shadow.

Synonyms: opaque, non-transparent

Antonyms: radiolucent, transparent