Several parts combine into one character.

案 is a phonetic-semantic compound: 安 (an, "peace / safety") + 木 (tree / wood). The original meaning was concretely physical: a wooden desk or low table on which one peacefully placed documents and ate meals. From this furniture origin grew an extended semantic chain: a desk → what one places on the desk (documents, agenda) → an item under consideration (a proposal, a bill) → mental projection (an idea, a plan). The same character covers physical desk and abstract proposal — and even mental projection.

Korean reading "an." 提案 (jean, proposal — basic business / political vocabulary), 法案 (beoban, legislative bill — used in news: "bill passes"), 答案 (daban, answer sheet — exam vocabulary), 議案 (uian, agenda item), 圖案 (doan, design / pattern — graphic design), 腹案 (bogan, "belly-plan" = an idea held secretly in mind / unannounced plan — used in Korean political reporting when leaders are believed to have undisclosed strategies).

Mandarin àn, 4th tone. 案 (àn), 答案 (dá'àn, the answer), 方案 (fāng'àn, plan / scheme — used for project plans: 实施方案 implementation plan), 档案 (dàng'àn, file / archive / record — central in Chinese bureaucracy: every Chinese citizen has a 个人档案 personal file maintained by employers and the government), 提案 (tí'àn, proposal — formal political proposal). 档案 deserves note: the personal-file system in mainland China can affect employment, residency, and benefits, making 档案 a uniquely loaded word.

Japanese on-reading アン (an) — 案 (an, plan / proposal — used standalone: いい案 ii an "a good plan"), 提案 (teian, proposal — business term: 提案書 teian-sho "proposal document"), 答案 (tōan, answer sheet), 法案 (hōan, bill / proposed law). And the most beloved Japanese compound: 案内 (annai, "internal-plan" = guidance / information / showing the way) — 案内 is the universal Japanese word for guiding someone, found everywhere: 道案内 (michi annai, road guidance / directions), 観光案内所 (kankō annai-jo, tourist information center), ご案内 (go-annai, "I will show you" — polite usage in hospitality). Japanese hospitality culture is built around 案内.

Memory aid: a wooden desk (木) where things rest peacefully (安) — what is placed on the desk became the proposal / agenda / plan.