adjective
1.
not inclined to give thanks
a thankless guest
Synonyms: unappreciative, ungrateful, unthankful
Related Word: self-centered; careless, heedless, thoughtless; unappreciative, ungrateful, unmindful
Contrasted words: appreciative, grateful, mindful; careful, heedful, thoughtful
Antonyms: thankful
2.
not likely to obtain thanks
a thankless job
Synonyms: unappreciated, ungrateful, unthankful
Related Word: disagreeable, distasteful, unpleasant; miserable, wretched
Contrasted words: thankworthy