What does diathermanous mean?
Diathermanous describes a material that allows radiant heat—infrared radiation—to pass through it. The word belongs chiefly to the vocabulary of physics and thermodynamics, where it distinguishes substances by how they interact with thermal radiation rather than with light in general. A classic illustration comes from early infrared experiments: rock salt is strongly diathermanous despite being only partly transparent to visible light, which made it a preferred material for prisms and windows in studies of heat radiation. Ordinary glass, by contrast, transmits visible light readily but absorbs much infrared radiation, making it comparatively poor at passing radiant heat. The opposite quality—blocking radiant heat—is termed adiathermanous. Though rarely encountered outside technical contexts today, the word remains useful for describing precisely why different transparent-looking materials behave very differently when heat, rather than light, tries to get through them.
adjective(Of a substance or medium) transparent to radiant heat; permitting the passage of infrared or thermal radiation while possibly blocking visible light.
- (Of a material) transmitting radiant heat; permeable to thermal radiation.
"Rock salt is notably diathermanous, allowing radiant heat to pass through even though it is opaque to much visible light."
"The physicist selected a diathermanous crystal so that infrared radiation could reach the detector behind it."
"Because ordinary glass is far less diathermanous than rock salt, early infrared experiments relied on salt prisms and windows."
A pane of glass can be crystal clear to your eyes yet nearly opaque to radiant heat — and 'diathermanous' is the physicist's word for materials that break that rule.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of diathermanous
Diathermanous derives from Greek elements: the prefix dia- meaning 'through' and thermē meaning 'heat', combined with an adjectival ending. It entered English in the nineteenth century amid the flourishing of research into radiant heat, when scientists such as Melloni needed precise vocabulary for materials' differing transparency to thermal rays. It shares its Greek root with words like thermal, thermometer, and isotherm, and sits alongside related coinages such as diathermic and diathermancy.
Related word forms
How diathermanous is actually used
A technical term used chiefly in physics, optics, and thermodynamics literature; rare in everyday speech and largely confined to older or specialized scientific texts.
Easily confused with diathermanous
Both mean permeable to heat, but diathermanous specifically concerns transmission of radiant heat (radiation), whereas diathermic more generally refers to conducting or transmitting heat.
Adiathermanous means the opposite of diathermanous — impervious to radiant heat.