Simultaneously, at the same time, as in All the boys jumped into the pool at one time. For synonyms, see at once, def. 1; at the same time, def. 1.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.