血 is a compound ideograph of striking simplicity: 皿 (a vessel / dish) with a single dot above it (a drop of blood). The picture documents an ancient ritual practice — the ceremonial vessel containing sacrificial blood used in oaths and treaties. The original Chinese term 歃血 (shàxuè, "to sip blood") referred to the ritual of swearing fidelity by drinking sacrificial blood from a shared vessel, a practice attested across pre-Han Chinese sources. The character preserves the religious gravity of blood as a sacred substance.

From this ritual origin, three semantic threads grew: blood as biological fluid, blood as commitment / oath, and blood as kinship / lineage.

Korean reading "hyeol." 血液 (hyeoraek, blood — formal medical term), 血壓 (hyeorap, blood pressure), 輸血 (suhyeol, blood transfusion), 血氣 (hyeolgi, "blood-energy" = vigor / hot-bloodedness, especially in youth), 血族 (hyeoljok, blood relatives / kinship), 血盟 (hyeolmaeng, blood oath / blood-sworn alliance). The full triad — medical, kin, oath — is alive in modern Korean.

Mandarin presents one of the most subtle 破音字 distinctions in everyday speech. xuè (4th tone) is the formal / written / scientific reading: 血液 (xuèyè, blood), 血压 (xuèyā, blood pressure), 血型 (xuèxíng, blood type). xiě (3rd tone) is the colloquial / spoken reading: 流血 (liúxiě, to bleed — said when you cut yourself), 血 alone in casual speech (xiě, often with diminutive 儿: 血儿 xiěr). The same character read formally as xuè or casually as xiě — one of the rare CJK examples where register alone distinguishes pronunciation.

Japanese on-reading ケツ (ketsu) — 血液 (ketsueki, blood), 血圧 (ketsuatsu, blood pressure), 輸血 (yuketsu, transfusion), 出血 (shukketsu, bleeding / hemorrhage). Kun-reading ち (chi) — 血 (chi, blood — everyday word), 血まみれ (chimamire, soaked in blood / bloody), 鼻血 (hanaji, nosebleed — note the rendaku from chi → ji). The Japanese saying 血は争えない (chi wa arasoenai, "blood cannot be argued with") means "you cannot deny your bloodline / heritage shows through." Like Korean, Japanese splits formal medical vocabulary (ketsu) from everyday usage (chi).

Memory aid: a single drop of blood above a sacrificial vessel — the ritual origin of the character.