Noun
しりあい
知り合いにたのんで、トーフグのコウイチからサインをもらいました。
I asked an acquaintance if they could get me Koichi’s autograph from Tofugu.
今知り合いにれんあい相だんしてるから、カラオケには行けないかも。ごめんね！
I’m consulting my acquaintance about my relationship with my boyfriend right now, so I probably won’t be able to join the karaoke party. Sorry!
ここだけの話なんだけど、上司が知り合いの人妻と浮気しているのよね。
Don’t tell a soul but my boss is having an affair with a married woman who is an acquaintance of mine.
You've probably seen the words 知る and 合う by now. This is someone you "know" because you have "come together" before, but that's pretty much it. You don't really know them well, you just met them a couple times so you know who they are. This person is an acquaintance.
The readings are that of 知る and 合う. So long as you know those words, you should be able to read this one too.