馬 is one of the most spectacularly preserved pictographs in the entire CJK system. Look at the oracle bone form: a horse seen in profile with its mane sticking up like flames, four legs distinctly drawn, a flowing tail at the back. Across three thousand years, the basic anatomy survived — even the modern 馬 still shows the four legs as four short strokes at the bottom. Mainland Chinese simplified 馬 to 马, dramatically reducing each leg to a single stroke and the mane to a hook, but the silhouette of a galloping horse is still visible if you squint.

As a radical, 馬 anchors the entire vocabulary of horse-related action: 騎 (qí, to ride), 駆 (qū, to drive / dash), 驚 (jīng, to be startled — like a horse spooked), 駅 (eki, station — originally a relay post for horses), 騒 (sō, noisy / restless).

Korean reading "ma." 競馬 (gyeongma, horse racing), 馬車 (macha, carriage), 騎馬 (gima, horseback riding), 木馬 (mongma, wooden horse — including the famous Trojan horse), and the elegant idiom 走馬看山 (jumagansan, "to look at mountains while galloping by" = to glance at something only superficially). Korean four-character idioms are richly populated with 馬.

Mandarin mǎ, 3rd tone (simplified 马). 马上 (mǎshàng, "on the horse" = "right away / immediately") — perhaps the most beautiful idiomatic compound in the language, capturing the urgency of someone setting off on horseback the moment they hear a request. 骑马 (qímǎ, to ride a horse), 马路 (mǎlù, "horse-road" = main street, a survival from the era when streets were measured by horse traffic). 马 is also the surname of one of China's most famous billionaires, Jack Ma (马云 Mǎ Yún).

Japanese on-reading バ (ba) — 競馬 (keiba, horse racing), 乗馬 (jōba, horseback riding). Kun-reading うま (uma) — 馬 (uma, horse), and the lovely 絵馬 (ema, "picture-horse" = small wooden plaques sold at Shinto shrines for writing wishes; visitors hang them in dedicated racks; the name comes from ancient practice of donating actual horses to shrines, which was later replaced by painted images). The everyday Japanese word for "fool" is 馬鹿 (baka, literally "horse-deer"), said to derive from a tale where a Qin dynasty courtier presented a deer and insisted to all that it was a horse — the test was whether anyone dared contradict him; those who agreed it was a horse "had become baka."

Memory aid: a side-view horse with mane, four legs, and tail — the picture is the meaning, preserved for three millennia.