Picture a small sign on a door or a table. It does not describe what is there; it tells you what does not happen there. Everything this word does comes from that sign — sometimes it is stuck on a room, sometimes on a person's way of living.
可以想成門上或桌上貼的一張小牌子。牌子不是在描述裡面有什麼，而是在說這裡「不會有」什麼。這個字的用法都從這張牌子長出來：貼在房間上，就是這裡不能抽菸；貼在人身上，就是這個人不抽菸；把牌子上那件事本身當成一個名字，就成了名詞用法。
From the word’s history
The source gives the word as non- plus smoking, with the noun back-formed from the adjective. The prefix does the whole job: it turns 'smoking' into 'the absence of smoking'.
資料來源指出，這個字是 non-（不、非）加上 smoking 造出來的，名詞用法則是從形容詞反推出來的。關鍵全在 non- 這個開頭：它把 smoking 翻成「沒有抽菸這件事」。英文裡 non-stop、non-profit 用的是同一招。
Wiktionary (kaikki extract), source_ref kaikki:3f6f69a190036ae4:1495562928:5517 — "From non- + smoking. The noun is back-formed from the adjective."
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