All at once; at the same time; doing many things together in a single action.
荷物を一度に運ぼうとすると大変だ。
It's hard if you try to carry all the luggage at once.
お願いを一度にたくさんされて、対応に困った。
I was asked for many favors all at once and didn't know how to handle them.
料理は一度に作りすぎると味が落ちることがある。
If you cook too much at once, the taste can sometimes suffer.