Pictograph: a central stalk with grains scattered to either side — rice grains shaken from a stalk during threshing. The character has barely changed since oracle bone times. Identical across 繁體 / 新字体 / 简体.

Rice is so foundational to East Asian civilization that 米 generated multiple unrelated meanings: — Rice as grain (the literal meaning) — The metric unit "meter" (米 chosen as phonetic match for "meter" in Mandarin and Japanese — 一米 = 1 meter, 米 in scientific Chinese) — America (米国 in Japanese, abbreviated form of アメリカ, choosing 米 as a phonetic match for "me-" in "America"; Korea uses 美 with the same logic — 미국 / 米國 vs 美國)

Mandarin: mǐ, dipping 3rd tone. 大米 (dàmǐ, rice / "big rice"), 米饭 (mǐfàn, cooked rice / a meal), 小米 (xiǎomǐ, "millet" — also famous as the Chinese tech brand Xiaomi), 玉米 (yùmǐ, corn — "jade rice"), 米尺 (mǐchǐ, meter ruler), 米国 (Měiguó — wait, no, China uses 美国 for USA, not 米国 — that's only Japan). Mandarin uses 米 for "meter" only in scientific writing.

Japanese: TWO on-readings. ベイ (bei) is dominant for "America" and rice in compounds — 米国 (Beikoku, USA — formal name in Japanese government documents, used parallel to アメリカ), 在米 (zaibei, residing in the USA), 玄米 (genmai, brown rice), 新米 (shinmai, new rice / new graduate / rookie). マイ (mai) appears in 白米 (hakumai, white rice). Kun-reading こめ (kome) is the everyday word — 米 (kome, rice grain), お米 (okome, rice — polite). Note 米 (kome, rice) vs 飯 (meshi / gohan, cooked rice) — Japanese distinguishes raw and cooked rice.

The Japanese name for the United States — 米国 (Beikoku, "Rice Country") — is one of the most quirky place-name spellings in any language. It survives because the 19th-century kanji-shorthand stuck.

Memory aid: rice grains scattered around a stalk — the East Asian dietary foundation made into a character.