Several parts combine into one character.

Compound ideograph: 八 (split / divide, from earlier batch) above 厶 (a stylized version of 私, "private / selfish"). The encoded meaning: "to divide private property equally" → "fair / public / common". The character was deliberately constructed as the OPPOSITE of 私 (sī / shi, "private / selfish"). Identical across 繁體 / 新字体 / 简体.

The public-vs-private opposition (公 vs 私) is one of the fundamental dichotomies in East Asian political and ethical thought.

Mandarin: gōng, level 1st tone. 公 anchors a major Mandarin business and public-life vocabulary: — 公司 (gōngsī, company) — THE word for "company / corporation" in modern Chinese; every Mandarin learner masters this early. — 公园 (gōngyuán, park) — public garden. — 公共 (gōnggòng, public) — 公共交通 = public transit. — 公平 (gōngpíng, fair). — 公开 (gōngkāi, openly / publicly). — 公斤 (gōngjīn, kilogram — "public weight" in metric system) — the metric system uses 公〜 prefix: 公里 (km), 公斤 (kg), 公分 (cm). — 办公 (bàngōng, do business / office work) — 办公室 (bàngōngshì, office).

Japanese: TWO on-readings. コウ (kō) is dominant — 公務 (kōmu, public service), 公開 (kōkai, public release), 公園 (kōen, park), 公共 (kōkyō, public), 公平 (kōhei, fair), 主人公 (shujinkō, protagonist — "the chief person of"). ク (ku) appears in some older compounds and titles. Kun-reading おおやけ (ōyake) is the formal native word for "public / official" — used in formal contexts: 公の場 (ōyake no ba, public setting), 公にする (ōyake ni suru, make public).

The Japanese 公 takes a striking grammatical role: as a name suffix, 〜公 means "Mr. / lord" (informal): 太郎公 (Tarō-kō, "Mr. Taro"). The chairman of a company is sometimes called 公 informally.

Memory aid: dividing one's private holdings — fairness encoded as anti-selfishness.