acquaintance

他是我们的一个熟人。

He's an ___acquaintance of ours.

我在会议上遇到他；他只是个熟人，不是亲密朋友。

I met him at a conference; he's just an ___acquaintance, not a close friend.

他对古典音乐有些了解，但称不上专家。

He has some ___acquaintance with classical music, but he's no expert.