thankless adj. + Add to list US //ˈθæŋkɫəs// UK //θˈæŋkləs// thank·less SynonymsAntonymsEtymology Synonyms unappreciatedungratefulungratifyingunthankful Antonyms gratefulOriginMEthankles→ENthankless From Middle English thankles, equivalent to thank + -less.