Of course in peak times like the summer holidays we do them every weekend, but at the moment it's usually once a month at most.
adv. once again;once more：又一次；再次
Once again British justice has appeared to falter.
She wanted to see him once more before she died.
adv. once and for all：彻底地；一劳永逸地
They had to be defeated once and for all.
adv. once in a while：偶尔；间或
Every once in a while we go to the cinema.
adv. once or twice：一两次；几次
She had been to London once or twice before.
adv. once removed：关系相隔一代的
a cousin once removed
adv. once upon a time：从前；很久以前；（用于谈论已不存在的状况，尤指过去的状况比现在的好）想当年
Once upon a time there were three princes.
Once upon a time, I wanted to change the world.
I met her once, briefly.
I've been to France once before.
Once a week
Once a month
Once every fortnight
Once every three months
Texas was once ruled by Mexico.
I knew him once.
My memory isn't as good as it once was.
if you once forget it
Once inside her flat, she opened the letter.
Once you have kids, your priorities change.
n. all at once：突然；忽然；同时；一起
All at once there was someone knocking on the door.
n. at once：立即；马上；同时；既…（又…）
I knew at once that something was wrong.
They all arrived at once.
Everybody is talking at once.
It was at once a question and a command.
n. for once：仅此一次；破例一次
She was able, for once, to relax.
n. just the once：只有一次
Can I borrow your car?—All right then, just this once.