夫 is a compound ideograph: 大 (a large standing figure of a person) plus a single horizontal stroke crossing the head — depicting a hairpin (簪) inserted into the topknot of an adult male. In ancient East Asian custom, a man's coming-of-age ceremony involved his hair being put up and pinned with a 簪. The character preserves this entire ceremony of 冠禮 (capping rite) in a single image: the adult man = the husband.

夫 forms the canonical pair with 妻 (wife), and the compound 夫妻 (married couple) anchors traditional marriage vocabulary across CJK.

Korean reading "bu." 夫婦 (bubu, married couple — formal Sino-Korean compound), 農夫 (nongbu, farmer — literally "farming-man"), 漁夫 (eobu, fisherman), 人夫 (inbu, laborer / worker). And distinctively in Korean and Japanese, the compound 工夫 (Korean gongbu, Japanese kufū) developed an unusual meaning: "to study / cram / learn through diligent effort" (Korean 공부) or "ingenuity / cleverness / contrivance" (Japanese kufū). This is one of the most striking semantic divergences in CJK history.

Mandarin fū, 1st tone. 夫 (fū), 丈夫 (zhàngfu, "ten-foot man" = husband — the everyday Mandarin word; "ten chi" was traditionally an adult man's height), 夫妻 (fūqī, husband and wife), 农夫 (nóngfū, farmer). And the famous false friend: 功夫 (gōngfu, "skill / time / effort / kung fu") — same compound 工夫/功夫 means three different things across CJK languages: Korean gongbu = study; Japanese kufū = ingenuity; Mandarin gōngfu = martial-arts skill / accumulated effort / time spent. The Mandarin sense gave the world the word "kung fu" through Bruce Lee films.

Japanese on-readings: フ (fu) — 夫婦 (fūfu, married couple), 農夫 (nōfu, farmer), 夫人 (fujin, married lady — used in 大統領夫人 daitōryō fujin "First Lady"), 工夫 (kufū, ingenuity / contrivance — divergent from Korean). フウ (fū) — appears in 夫婦 (fūfu). Kun-reading おっと (otto) — 夫 (otto, one's own husband — formal-ish, paralleling 妻 tsuma). Japanese also uses 旦那 (danna) and 主人 (shujin) for "husband" with different politeness registers.

Memory aid: a large person (大) with a hairpin on top — adult man, husband. Compare 工夫 in Korean (study) vs Japanese (ingenuity) vs Mandarin (kung fu / skill).