1. (a.) Not acknowledging favors; not expressing thankfulness; unthankful; ungrateful.

2. (a.) Not obtaining or deserving thanks; unacceptable; as, a thankless task.

bitter bootless careless despised disagreeable dislikable disliked displeasing distasteful fruitless futile heedless lowly miserable misprized misunderstood out of favor profitless self-centered sour thoughtless ugly unacknowledged unalluring unappealing unappetizing unappreciated unappreciative unattractive uncared-for undelectable undelicious undesirable unengaging unenjoyable ungrateful uninviting unlamented unlikable unmindful unmissed unmourned unpalatable unpleasant unpleasing unpopular unprofitable unregretted unrequited unrewarding unsavory unsung untasteful unthankful unvalued unwelcome useless vain wretched