Several parts combine into one character.

Phonetic-semantic compound: 月 (flesh-radical) + 宛 (to bend, providing phonetic value). The encoded meaning: "the bending part of the body" → arm. Identical across 繁體 / 新字体 / 简体.

Mandarin: wàn, falling 4th tone. In modern Mandarin, 腕 typically refers specifically to the WRIST, while the colloquial word for "arm" is 胳膊 (gēbo). 手腕 (shǒuwàn, wrist OR figuratively "skill / artifice / political maneuvering"). 大腕 (dàwàn, "big wrist" → top star / heavyweight in entertainment industry — modern slang). So the Mandarin sense narrowed to "wrist + skill".

Japanese: on-reading ワン (wan) — 手腕 (shuwan, ability / skill — same compound, similar meaning to Mandarin), 鉄腕 (tetsuwan, "iron arm" — strong arm / pitching arm; also the title of Astro Boy 鉄腕アトム). Kun-reading うで (ude) is the everyday word and broader than Mandarin's 腕 — 腕 (ude) covers the WHOLE arm in Japanese, not just wrist. Compounds: 腕時計 (udedokei, wristwatch — "arm-watch"), 腕前 (udemae, skill / ability), 腕白 (wanpaku, mischievous boy — irregular reading).

The Japanese 腕 carries a metaphorical sense of "skill / ability" alongside the physical body part — same as Mandarin and Korean. 腕がいい (ude ga ii, "the arm is good") means "skilled / talented", used for craftsmen, athletes, doctors. 腕が上がる (ude ga agaru, "the arm goes up") means "skill improves".

The metaphor "arm = skill" runs across CJK languages, paralleling English idioms like "to flex one's arm".

Memory aid: flesh + bending = the body's flexible arch — the arm.