知合い
しりあい · shiriai · JLPT N3 · noun
acquaintance
🤝 知り合い = know (shiri) + each other (ai): people who know each other
知 is the stem of 知る (shiru, to know) and 合い comes from 合う (au, to do mutually). Knowing that goes both ways gives you an acquaintance. The same 合い appears in 話し合い (talking together, a discussion).
合 — 乛 (lid/roof) + 口 (mouth)
Originally a pictograph of a lidded vessel — a cover (亼) closing over an opening (口) — giving the core sense of 'come together, join, fit.' From 'fit/match' it extended to 'combine, unite, agree' and to measure-word uses. The reading hé reflects this 'joining' meaning.