Picture the half-second inside a magician's hand. The coin never left the room; it simply moved faster than your eye, at the one moment you happened to be looking somewhere else. You watched the whole time and still missed the only part that mattered. Sleight is an old English word for skill or cunning, so the phrase is literally 'skill of the hand' - and that missed half-second is what the phrase is really about, wherever it turns up.
From the word’s history
From Middle English slegthe of hande, literally 'sleight (skill, cunning) of hand'. Old French had the parallel léger de main, 'light of hand', which English borrowed whole as legerdemain. Both phrases name the hand and the skill and nothing else - the deception is what the skill is used for, not what the words say.
來自中古英文的 slegthe of hande，字面就是「手的巧技」。古法文有個平行說法 léger de main（手輕），英文整個借過來寫成 legerdemain。兩個說法點名的都只是「手」和「技巧」，騙人是這個技巧的用途，不是字面的內容。
Wiktionary entry 'sleight of hand', etymology (packet evidence kaikki:3f6f69a190036ae4:1014724545)
登入就可以看每一支怎麼連回核心畫面。