Thanklessness (11)
I believe the answer is:
ingratitude
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">thanklessness</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ingratitude that I've seen before include "Thanklessness" , "Lack of appreciation" , "Inappreciativeness" , "base behaviour" , "Ungratefulness" .)