someone you know, but who is not a close friend:
somebody you know[countable]
She was a casual acquaintance of my family in Vienna.
He heard about the job through a mutual acquaintance (=someone you and another person both know).
a relationship with someone you know, but who is not a close friend:
They developed an acquaintance over the Internet.
You can't judge her on such short acquaintance (=when you have not known her long).
My uncle did not improve on further acquaintance (=when you knew him better).
to meet someone for the first time:
I should be delighted to make Mrs McGough's acquaintance.
At the hotel, I made the acquaintance of a young American actor.
knowledge or experience of a particular subject
The practice of a lawyer requires acquaintance with court procedures.
have a passing/nodding acquaintance with something (=have only slight knowledge or experience of something)
He has a passing acquaintance with a lot of different subjects.
a person of your acquaintance is someone that you know:
The poems were written by various women of her acquaintance.
when you meet someone for the first time:
Most people are nicer than you think on first acquaintance.