Several parts combine into one character.

治 is a phonetic-semantic compound: 氵 (water) + 台 (tái, originally a stand or platform — providing the sound). The original meaning was specifically a river name (治水, the Zhi River) — and from that hydronym grew the verb "to manage water flow / control rivers." This was no small matter: in ancient China, controlling floods and irrigation was the foundational task of statecraft. The mythological emperor 禹王 (Yu the Great) is said to have founded the Xia dynasty through his masterful 治水 (zhìshuǐ, "river control"), and that very act of directing waters became the metaphor for all governance. Hence the semantic chain: managing water → managing a country → curing disease (managing the body's internal flows).

治 is one of the most philosophically loaded characters in East Asia. The Confucian classic 大學 (Daxue) outlines the path of cultivation as 修身齊家治國平天下 ("cultivate the self, regulate the family, govern the state, bring peace to all under heaven") — placing 治國 (zhì guó, "governing the state") as the third stage of self-development.

Korean reading "chi." 政治 (jeongchi, politics), 治療 (chiryo, medical treatment — the body sense), 統治 (tongchi, rule / governance), 治安 (chian, public security / law and order), 自治 (jachi, self-governance / autonomy — used in 자치단체 jachi danche "local autonomous government"), 治家 (chiga, household management). The character spans politics and medicine seamlessly.

Mandarin zhì, 4th tone. 治 (zhì), 治理 (zhìlǐ, governance / management — used in modern Chinese political vocabulary), 治疗 (zhìliáo, medical treatment), 政治 (zhèngzhì, politics), 自治 (zìzhì, autonomous), 治国 (zhìguó, "governing the state"). The Confucian phrase 治国平天下 remains a cultural touchstone in Mandarin political writing.

Japanese on-readings split semantically. ジ (ji) covers governance: 政治 (seiji, politics), 自治 (jichi, autonomy), and the famous era name 明治 (Meiji, "enlightened rule" 1868-1912 — Japan's modernization era). チ (chi) covers medicine and security: 治療 (chiryō, treatment), 統治 (tōchi, rule), 治安 (chian, public order). Kun-readings: 治める (osameru, "to govern / manage"), 治る (naoru, "to heal / recover from illness"), 治す (naosu, "to heal / cure"). Critical homophone caution: なおる takes different kanji depending on what is being healed. 治る = the body recovers from illness; 直る = something broken gets fixed (a machine, a habit). The 治/直 split is essential Japanese kanji literacy.

Memory aid: water (氵) being managed (台) — controlling rivers became the metaphor for governing a country and healing a body.