～口
～くち · ～kuchi · JLPT N2 · noun
opening
🚪👄 口 = mouth: an opening that things go in and out of
口 (kuchi) means mouth, and a mouth is where things enter and leave. As a suffix it marks an opening: 入口 (iriguchi) = enter + mouth = entrance; 出口 (deguchi) = exit + mouth = exit. Note that kuchi often softens to guchi.
口 — pictograph of an open mouth
口 is one of the oldest pictographs in Chinese, originally drawn as a simple outline of an open mouth. Its core meaning 'mouth' extended naturally to 'opening' or 'entrance', as in 入口 (entrance). It also serves as a common radical in characters related to speech, eating, or apertures.