Function, purpose (3)
I believe the answer is:
use
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">function</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(something's use is its function)</span><br/ ><br/ >'<span class="explanation-format__original">purpose</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that purpose can be written as use)</span><br/ ><br/ ></span>
(Other definitions for use that I've seen before include "Employment; utilise" , "Put to a particular purpose" , "Sue for employment" , "Employ (something)" , "Expend in amusement" .)