核心畫面
The word is the sound. A finger goes up to the lips, the air out, and the noise in the room is supposed to stop. Everything shush does grows out of that one breath: it is the noise you make, and it is also the thing you do to somebody else.
可以想成嘴巴發出的那一聲「噓」：手指豎在唇上，氣音一出，旁邊的聲音就該停下來。這個字本身就是那個聲音寫成的。所以它同…更多收起
可以想成嘴巴發出的那一聲「噓」：手指豎在唇上，氣音一出，旁邊的聲音就該停下來。這個字本身就是那個聲音寫成的。所以它同時是你喊出來的那一聲，也是你對別人做的那個動作——兩個用法其實是同一口氣。From the word’s history
The source describes the word simply as imitative, and points to shh and hush as the same kind of formation. The word does not come from anywhere; it is a written-down noise.
來源資料把這個字標為擬聲，並把 shh 和 hush 列為同一類。也就是說它沒有更早的來源，它就是一個被寫下來的聲音。
Wiktionary entry 'shush', verb, etymology note 'Imitative. Compare shh and hush.' (packet evidence kaikki:3f6f69a190036ae4:1159904240)