口袋
kǒudài · HSK 4
👖 口袋 = 口 (mouth/opening) + 袋 (bag) — a bag with an opening
口 means mouth or opening, and 袋 means bag or sack. A pocket is literally an opening-bag sewn onto clothing. 袋 also shows up in 手袋 (handbag) and 睡袋 (sleeping bag).
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.
袋 — 代 (dài, phonetic) + 衣 (clothing)
袋 is a semantic-phonetic compound. The bottom 衣 'clothing/cloth' gives the meaning, since bags were originally made of cloth, while 代 on top supplies the sound 'dài'. It has long meant 'bag, sack, pouch'.