What does athermanous mean?
Athermanous is a technical adjective from physics describing a substance that does not transmit radiant heat — that is, one which blocks or absorbs thermal radiation rather than allowing it to pass through. A body of water, for instance, behaves in ways that can be described as athermanous with respect to certain wavelengths of infrared light, and early experimenters used athermanous screens to test how much heat different materials could intercept. The term is the direct opposite of 'diathermanous,' which refers to media such as rock salt that readily admit radiant heat. Formed from Greek roots meaning 'without heat,' the word belongs chiefly to the vocabulary of classical optics and thermodynamics: it appears rarely outside textbooks, lecture notes, and histories of science, but it remains a precise and useful label when discussing the transparency of materials to infrared radiation.
adjectiveNot permitting the passage of radiant heat; opaque to thermal radiation.
- (Of a substance or medium) impermeable to radiant heat; not transmitting infrared radiation.
"The athermanous coating of the flask kept the coffee hot for hours."
"Rocksalt is diathermanous, while ordinary glass behaves as an athermanous barrier to far-infrared radiation."
"The experimenter placed an athermanous screen between the lamp and the thermopile, and the reading dropped to zero."
In Victorian physics lectures, 'athermanous' was the word that decided whether sunlight warmed your skin — it literally means 'no heat gets through.'
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of athermanous
Athermanous derives from Greek roots: the negative prefix 'a-' ('not') combined with 'thermē' or 'thermos' ('heat'), plus an adjectival suffix. It entered English in the nineteenth century as physicists studying radiant heat needed terms to distinguish materials that block thermal radiation from those that transmit it, alongside the parallel formation 'diathermanous.' Its Greek root also underlies familiar words such as 'thermal,' 'thermometer,' and 'isotherm.'
How athermanous is actually used
Primarily a technical term of nineteenth- and twentieth-century physics, now largely confined to historical and specialist contexts; it sounds formal and scientific rather than conversational.
Easily confused with athermanous
Diathermanous means the opposite — transmitting radiant heat rather than blocking it.