athermanous,a.Physics.|əˈθɜːmənəs| [f.Gr. ἀ priv. + θερµαν- stem of θερµαίν-ειν to heat (f. θέρµη heat) + -ous.] Not permeable by radiant heat. 1863Tyndall Heat iii. 79 An athermanous body which stops the radiation.1871B. Stewart Heat §206 This substance is..athermanous, that is to say opaque for heat.