Process of dying out (10)
I believe the answer is:
extinction
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">process of dying out</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for extinction that I've seen before include "Death of a species" , "Complete annihilation" , "Process of dying out" , "Dying-out" .)