Climb or ascend (5)
I believe the answer is:
mount
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">climb</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that climb can be written as mount)</span><br/ ><br/ >'<span class="explanation-format__original">ascend</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(mounting is a kind of ascending)</span><br/ ><br/ ></span>
(Other definitions for mount that I've seen before include "seat" , "- - Sinai" , "put on launch" , "The height" , "Climb - eg Everest" .)