Entry 1 sense Webster, 1913 Thermodynamics /thẽrmˌ-ōd-īnˌ-ăm'-ĭks/ · Ther·mo·dy·nam·ics · IPA /ˌθɜː(ɹ)moʊdaɪˈnæmɪks/ 01 n. The science which treats of the mechanical action or relations of heat. 1. The science which treats of the mechanical action or relations of heat.