Once

Once is an adverb or conjunction.

Once as an adverb

We use once as an adverb to mean ‘one single time’:

I’ve only met Jane’s husband once. (one time)

We say once a + singular time expression and once every + plural time expression to talk about how often something happens:

They go for dinner together oncea month. (one time per month)

Not: They go for dinner once the month.

I see him once every two or three weeks.

We also use once to mean ‘at a time in the past but not now’. In this meaning, we often use it in mid position (between the subject and the main verb, or after the modal verb or first auxiliary verb, or after be as a main verb):

My father once worked on an oilrig. (He no longer works there.)

The Millers once owned a dairy farm. (They no longer own a dairy farm.)

She was once a schoolteacher but she hated it.

The phrase once upon a time is used at the start of children’s stories. We sometimes use it to mean ‘long ago’:

Once upon a time there was a little girl called Little Red Riding Hood …

You used to go to nightclubs once upon a time!

Once as a conjunction

We use once as a conjunction meaning ‘as soon as’ or ‘after’:

Once I’ve picked Megan up, I’ll call you.

My boss is a nice man once you get to know him.

We don’t use shall or will in the clause with once:

Once I pass all my exams, I’ll be fully qualified.

Not: Once I will pass …