裏口
うらぐち · uraguchi · JLPT N2 · noun
back door
🚪 裏口 = back side (ura) + mouth/opening (kuchi → guchi)
裏 ura means the back or reverse side, as in 裏切る uragiru, to betray (to cut from behind). 口 kuchi means mouth or opening, and it softens to guchi in compounds. So a back-side opening is a rear entrance. Compare 入口 iriguchi, entrance.
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.