At once Definition 1 of 2Pro Tip 1/3Urgency Connotation Conveys a sense of urgency and the need for quick action or response. Please send help at once! Pro Tip 2/3Strong Command Often used to issue commands, showing authority or seriousness. Stop that at once! Pro Tip 3/3Casual Tone Can be used informally among friends or family to express need for haste. Come over at once, we're cutting the cake.