手 is a hand with five fingers spread, drawn flat. Oracle bone forms show the splay of the digits and the wrist arc clearly. Identical across 繁體 / 新字体 / 简体.

Like 水 and 火, the hand has a critical positional variant. When 手 sits on the left of a compound character, it flattens into 扌 (the "hand radical"). Once you spot 扌 you can predict the meaning involves a manual action: 打 (strike), 拍 (clap), 握 (grasp), 投 (throw), 拉 (pull), 推 (push), 持 (hold), 掃 (sweep), 拭 (wipe). This is one of the highest-yield radicals in the script — easily a third of common verbs use it.

Mandarin: shǒu, dipping 3rd tone. 手 covers physical hand and metaphorical "agent / specialist" alike: 手机 (shǒujī, cellphone — "hand-machine"), 手表 (shǒubiǎo, wristwatch), 握手 (wòshǒu, handshake), 高手 (gāoshǒu, expert — "high hand"), 选手 (xuǎnshǒu, contestant), 杀手 (shāshǒu, assassin), 歌手 (gēshǒu, singer). The "hand = practitioner" metaphor runs through every CJK language.

Japanese: on-reading シュ (shu) in 手術 (shujutsu, surgery), 握手 (akushu, handshake), 選手 (senshu, athlete). The kun-reading て (te) is the everyday word — 手 (te, hand), 手紙 (tegami, letter — "hand paper"), 上手 (jōzu, skillful — "upper hand"), 下手 (heta, unskillful — "lower hand"), 切手 (kitte, postage stamp — "cut hand", an old printing-block term).

Memory aid: a hand turned palm-down, the four fingers visible. The horizontal strokes are the fingers; the long vertical sweep is the arm.

In Japan·편지 (手紙 = てがみ)

In China·화장지 (手紙 = shǒuzhǐ)