say it: THANG-kluhs
thankless is an adjective meaning "not feeling or showing gratitude". It carries 2 recorded senses.
not feeling or showing gratitude
“ungrateful heirs”
“How sharper than a serpent's tooth it is / To have a thankless child!”
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for thankless come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.