standby comes straight out of stand by — to stand beside a thing instead of inside it. One way to hold it: a person waiting in the wings of a stage. Not performing, and not gone home. Dressed, in place, watching, able to walk on the second someone calls. Everything the word does is a version of that pose: a nurse waiting for the phone, a passenger waiting for a seat, a tin of milk waiting in the , a television waiting behind its little red light.
From the word’s history
Wiktionary records standby as a deverbal noun formed from the phrasal verb stand by — the noun is the act of standing by, frozen into a thing. That literal picture of standing beside is still doing the work in every modern use.
Wiktionary 的 standby 條目寫 Deverbal from stand by，也就是這個名詞是直接從動詞片語 stand by 變來的：把「站在旁邊」這個動作凍成一個東西。今天所有的用法，底下都還是那個站在旁邊的畫面。
Wiktionary (kaikki extract kaikki:3f6f69a190036ae4:741028534), standby noun, etymology field: Deverbal from stand by.
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