At one time, at one time (4)
I believe the answer is:
erst
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">at one time at one time</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 erst that I've seen before include "At first; formerly" , "in former times" , "in the past" , "Rest turned formerly" .)