开口
kāikǒu · HSK 7
open one's mouth
👄 开口 = 开 open + 口 mouth, so to open the mouth (or open up a bottle/blade edge)
口 is the square mouth/opening glyph; 开 means open. Together they literally mean open the mouth, which extends to start speaking, uncork a bottle, or grind a fresh cutting edge onto a blade.
开 — two hands 廾 + door 门 (open gate)
Originally written 開, showing two hands (廾) lifting the bar (一) off a gate (門) to open it. The simplified form 开 keeps the two-hands element and drops the gate. Core meaning 'to open' extended to 'start, operate, bloom'.
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.