You can think of dictation as words travelling straight out of one mouth and onto someone else's page, with nothing changed on the way. One person owns the words; the other person only catches them. Hold that picture and the school exercise is the same event with a teacher at one end and a class at the other — and the 'orders' meaning is the same shape again, with the words replaced by instructions you are expected to take down and obey.
From Late Latin dictatio, a noun of action from dictare 'to say repeatedly'. By surface analysis it is simply dictate + -ion.
來自晚期拉丁文 dictātiō，是動作名詞，源頭是 dictāre「一再地說」。從表面看就是 dictate 加上 -ion。這條線索正好對上核心畫面：口述的人往往要慢慢說、重複說，好讓對方跟得上。
Wiktionary etymology supplied in this packet (kaikki:3f6f69a190036ae4:636699266) for 'dictation': Late Latin dictātiō < dictātus < dictō; by surface analysis dictate + -ion
From the picture
我說，你照辦
口述的那一幕裡，寫的人沒有插嘴的餘地：說什麼就記什麼。把這層關係從紙上搬到人身上，接住的東西從「字」換成「指示」，就成了這個意思。所以 under dictation 是照別人的意思做事，自己的判斷被擱在一邊，而且說話的人通常帶著不滿。這是概念上的延伸讀法，不是說歷史上一定照這個順序發展。
noun · C1
The giving of orders that other people are simply expected to obey; often used when the orders come from outside or from above, and are handed down in a way that leaves no room to answer back.
命令；擺布
noun · B1
The act of saying words out loud, at a speed that lets another person write or type them down exactly as they were said.
口述
noun · B1
A piece of writing that a teacher reads out loud so that the class can write down what they hear; it tests whether you can catch the words and spell them correctly.
聽寫（測驗）