1 [count] : someone who is known but who is not a close friend • Is he an acquaintance of yours? [=have you met him?] • She ran into an old acquaintance at the grocery store. • My wife and I met through a mutual acquaintance. [=a friend introduced us to each other] • a casual acquaintance
2 [noncount] formal : the state of knowing someone in a personal or social way : the state of knowing someone as an acquaintance • our family’s close acquaintance with our neighbors • It’s a pleasure to make your acquaintance. [=(less formally) it’s nice to meet you.] • She struck up an acquaintance with a man from the city. • a doctor of my acquaintance [=a doctor that I know] • He seemed cold at first, but on closer/further acquaintance I realized that he was just shy.
3 : knowledge about something — followed by with [singular] • She has only a nodding/slight/superficial acquaintance with the facts of the case. [=she knows only a little about the facts of the case] • He has more than a passing acquaintance with wine. [=he knows a lot about wine] [noncount] • While he has some acquaintance with the subject, he is not an expert.