made familiar with; accustomed to: I am used to hitchhiking.
(takes an infinitive or implied infinitive) used as an auxiliary to express habitual or accustomed actions, states, etc, taking place in the past but not continuing into the present: I don’t drink these days, but I used to; I used to fish here every day.
Usage: The most common negative form of used to is didn’t used to (or didn’t use to), but in formal contexts used not to is preferred
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
If something used to /juːs tuː, juːs tə/ happen, it happened regularly in the past but does not happen now. Similarly, if something used to be true, it was true in the past but is not true now.
She used to go swimming every day.
I used to be afraid of you.
In conversation, you can say that something didn’t use to happen or didn’t use to be true.
The house didn’t use to be so clean.
Many people use the form didn’t used to instead of didn’t use to. However, some people think that this use is incorrect.
They didn’t used to mind what we did.
You can also say that something never used to happen or be true.
Where I lived before, we never used to have posters on the walls.
Snooker and darts never used to be shown on television.
You can also say that something used not to happen or be true. This is a fairly formal use.
It used not to be taxable, but now it will be subject to tax.
In standard English you don’t say that something ‘usedn’t to‘ happen or be true.
You form yes/no-questions with used to by putting did in front of the subject, followed by use to.
Did you use to do that, when you were a kid?
Many people use the form used to instead of use to in questions. However, some people think that this use is incorrect.
Did you used to live here?
Used to can also be used in wh-questions. If the wh-word is the subject of the clause, or part of the subject, you put used to after it, without an auxiliary verb.
What used to annoy you most about him?
If the wh-word is the object of the clause, or part of the object, you use the auxiliary verb do after it, followed by the subject and used to.
What did you used to do on Sundays?
Used to has another meaning. If you are used to something, you have become familiar with it and you accept it. With this sense, used to is preceded by the verb be or get, and is followed by a noun or an -ing form.
It doesn’t frighten them. They‘re used to it.
I‘m used to getting up early.
It’s very noisy here, but you’ll get used to it.
Collins COBUILD English Usage © HarperCollins Publishers 1992, 2004, 2011, 2012