Picture the one person standing high up on the lookout tower while everyone else sleeps. Nothing has happened yet — that is the point. Their eyes are open, their body is turned outward, and they are ready to shout the moment something moves on the horizon. Every use of `alert` keeps a piece of that : the person who is watching, the shout they give, and the state a whole town is in once the shout has gone out.
From the word’s history
From French alerte (17c.), from the phrase a l'erte, "on the watch", from Italian all'erta, literally "to the height" — erta being a lookout or high tower (ultimately from Latin erigere, "to raise"). It entered English as an adverb in the 1610s meaning "on the watch", became an adjective by 1712, a noun in 1796 ("attitude of vigilance", as in on the alert) and then "a warning report" by 1803, and a verb by 1864. The English phrase on the alert is a direct fossil of the original Italian all'erta — literally, up on the lookout tower.
alert 來自法語 alerte（17 世紀），源頭是片語 a l'erte「在守望中」，而這又來自義大利語 all'erta，字面意思是「到高處去」——erta 指的是瞭望點、高塔（最終來自拉丁語 erigere「升起」）。它進入英文的順序很清楚：1610 年代先是副詞「在守望著」，1712 年成為形容詞，1796 年變成名詞（指「戒備的狀態」，也就是 on the alert 這個說法），1803 年才多出「警報」的意思，1864 年再成為動詞。所以英文的 on the alert 其實就是義大利語 all'erta 的化石：字面上真的是「站在瞭望塔上」。
Online Etymology Dictionary, entry "alert" (etymonline.com/word/alert)
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原始詞典資料10 筆記錄
以下是外部詞典記錄的用法，摘錄並精簡格式，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
Alertname
- 1
A community in the Qikiqtaaluk Region, Nunavut, Canada; the northernmost permanently inhabited place in the world.
- 2
An alternative name for Alharod, a village in Varzaqan County, East Azerbaijan Province, Iran.
- 3
An unincorporated community in Jackson Township, Decatur County, Indiana, United States.
alertadj詞源 1/əˈlɜːt/
- 1
Attentive; awake; on guard.
- 2
obsoletebrisk; nimble; moving with celerity.
- I saw an alert young fellow that cocked his hat upon a friend of his who entered just at the same time with myself
alertnoun詞源 1/əˈlɜːt/
- 1
An alarm.
- 2
A notification of higher importance than an advisory.
- 3
governmentmilitarypoliticsA state of readiness for potential combat.
- an airborne alert; ground alert
- 4
computingengineeringmathematicsSynonym of bell (“bell character”).
alertverb詞源 2/əˈlɜːt/
- 1
To give warning to.
摘錄自 英文維基詞典 English Wiktionary，已精簡格式；依 CC BY-SA 4.0 授權使用，改動後的內容同樣以此授權提供。