at once
1.very soon; immediately立刻
The telegram must be sent at once.电报必须立即发出。
I recognized him at once.我立刻就认出了他。
2.both; equally同样;兼
He is at once a statesman and a writer.他既是一位政治家,也是一位作家。
He was at once happy and sad.他悲喜交集。
The book is at once interesting and instructive.这本书既有趣又有教育意义。