Extend an arm (5)
I believe the answer is:
reach
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">extend an arm</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for reach that I've seen before include "range" , "Put out the hand for a part of the river" , "Arrive at (a place)" , "Attain; extend to" , "Come up to - stretch between bends" .)