Altogether means ‘completely’.
The noise had stopped altogether.
We need an altogether different plan.
You also use altogether to show that an amount is a total.
You will get £340 a week altogether.
Don't confuse altogether with all together. You use all together to say that a group of people or things are together or do something together, and that none of them is missing.
It had been so long since we were all together – at home, secure, sheltered.