<p><strong>Adjective</strong></p><ul><li>not likely to be appreciated or rewarded; unappreciated: a thankless job.</li><li>not feeling or expressing gratitude or appreciation; ungrateful: a thankless child.</li></ul><p><strong>Synonyms</strong></p><ul><li>profitless</li><li>unrewarding</li><li>unacknowledged</li><li>vain</li></ul>