At one time in the past (4)
I believe the answer is:
once
(Other definitions for once that I've seen before include "not repeatedly" , "Previously" , "At some former time" , "Formerly - not repeated" , "In days past" .)
I believe the answer is:
once
(Other definitions for once that I've seen before include "not repeatedly" , "Previously" , "At some former time" , "Formerly - not repeated" , "In days past" .)