English English Wikipedia has an article on:euthyroid sick syndromeWikipedia Noun euthyroid sick syndrome (uncountable) A state of adaptation or dysregulation of thyrotropic feedback control wherein the levels of T3 and/or T4 are abnormal, but the thyroid gland does not appear to be dysfunctional. Synonym: (initialism) ESSWikiwand - on Seamless Wikipedia browsing. On steroids.