By oneself (5)
I believe the answer is:
alone
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">by oneself</span>' is the definition.<br/ ><span class="explanation-format__explanation">(being by oneself is being alone)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for alone that I've seen before include "With no one to see" , "without another" , "Without anybody or anything else" , "Singly" , "On one's own" .)