The inherent quality or state of being diathermal; the capacity or tendency to allow heat to pass through without absorption.
From Greek 'dia-' (through) + 'thermē' (heat) + '-aneity' (Latin suffix indicating abstract quality), a highly technical term from 19th-century thermal physics.
This is one of those delightfully long scientific terms that basically means 'the property of being see-through to heat'—it's the kind of word that makes science sound more mysterious than it actually is.
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