Several parts combine into one character.

午 was originally a picture of a pestle. Later it came to mark the seventh animal of the twelve Earthly Branches — the Horse — and the hour when the sun stands at the center of the sky: noon. In the old timekeeping system the hour of 午 (11 a.m.–1 p.m.) is when the sun is highest.

Mandarin: wǔ, 3rd tone. 中午 (zhōngwǔ, noon), 上午 (shàngwǔ, morning / a.m.), 下午 (xiàwǔ, afternoon / p.m.), 午饭 (wǔfàn, lunch). The zodiac Horse is also 午 — 午马 (wǔmǎ).

Japanese: on-reading ゴ (go), kun うま (uma, horse). 午前 (gozen, a.m.), 午後 (gogo, p.m.), 正午 (shōgo, noon), 子午線 (shigosen, meridian). In Japanese tradition the direction of 午 (the Horse) is due south.

Korean hanja-sound "o": 午前 (ojeon, a.m.), 午後 (ohu, p.m.), 正午 (jeongo, noon), 端午 (Dano, the fifth-month festival). Because 午 (noon) faces 子 (midnight) exactly opposite, the word 子午線 (jaoseon, meridian / the line of longitude) was born here.

Memory aid: the sun standing at the middle of the sky at midday — the exact opposite of 子 (midnight).