Once vs Simultaneously

When to use each in English, with meaning, register, and examples.

	Once	Simultaneously
Meaning	one time	At the same time as something else.
CEFR level	A1	C1
Part of speech	adverb	adverb
Usage notes	Use 'once' to refer to something happening a single time in the past. It's neutral and often used in storytelling. It wouldn't be appropriate in highly formal writing.	Use 'simultaneously' to describe two or more actions happening at the same time. It works well in both spoken and written contexts but may sound overly formal in casual conversation.

Frequently asked questions: Once vs Simultaneously

What's the difference between "Once" and "Simultaneously"?

"Once" means: one time "Simultaneously" means: At the same time as something else.

When should I use "Once" and "Simultaneously"?

They can all be used in everyday English.

Are "Once" and "Simultaneously" the same CEFR level?

"Once" is at A1, "Simultaneously" is at C1 on the CEFR scale.