1.
If you are ~ with something, you know about it because you have learned it or experienced it. (FORMAL)
He was well ~ with the literature of France, Germany and Holland...
= familiar
ADJ: v-link ADJ with n
2.
If you are ~ with someone, you have met them and you know them. You can also say that two people are ~. (FORMAL)
No-one personally ~ with the couple was permitted to talk to the Press...
It’s true we were ~, but no more than that.
ADJ: v-link ADJ, usu ADJ with n
3.
If you get or become ~ with someone that you do not know, you talk to each other or do something together so that you get to know each other. You can also say that two people get or become ~.
The meetings were a way to get ~ with each other.
ADJ: v-link ADJ, oft ADJ with n
4.
see also acquaint