安靜、不張揚的樣子
形容詞的兩個意思，都是畫面裡「已經安定下來」的狀態：一個講整體氣氛，一個講移動的速度。
adjective · C1
Calm, quiet and a little serious, with nothing loud, fast or showy about it. It can describe a person, a place, an event, a building, or a piece of writing.
沉靜的；不熱鬧的
核心畫面
One way to hold this word: something that was up and moving has settled and sat down. Picture a room where everyone is seated and talking softly, or dust that has stopped swirling and come to rest on a table. Nothing is rushing, nothing is loud, nothing is bright. From that picture you get a person whose manner stays even, a town where the shops close at six, a walk that never speeds up, and the drug a doctor gives someone so that the fear or the pain settles too.
一種想法是：本來浮著、動著的東西，安定下來坐好了。可以想像一個大家都坐著、小聲說話的房間，或是原本飛舞的灰塵，慢慢落…更多收起
一種想法是：本來浮著、動著的東西，安定下來坐好了。可以想像一個大家都坐著、小聲說話的房間，或是原本飛舞的灰塵，慢慢落到桌面上不動了。沒有人在趕，沒有聲音很大，也沒有什麼是搶眼的。從這個畫面出發，就有了舉止穩定的人、六點就打烊的小鎮、從頭到尾不加速的步伐，也有了醫生給的那一針——讓恐懼和疼痛也跟著沉下來。From the word’s history
Latin sēdātus (calm, composed) comes from the verb sēdō (to calm, to settle, to stop), and behind that lies the very old root meaning to sit. The verb sedate comes from the same Latin verb. So the settling-down picture is sitting inside the word's history, not only in the modern meanings.
拉丁文 sēdātus（平靜的、沉著的）來自動詞 sēdō（使安定、平息、停下來），再往上是一個很老的字根，意思是「坐」。動詞 sedate 也是從同一個拉丁動詞來的。所以「讓它定下來」這個畫面，本來就在這個字的來歷裡，不只是現代用法的比喻。
Wiktionary entry for sedate, source_ref kaikki:3f6f69a190036ae4:924793199 (adjective) and kaikki:3f6f69a190036ae4:924820671 (verb): Late Middle English sedate, from Latin sēdātus, participial adjective of sēdō, ultimately from Proto-Indo-European *sed- (to sit); the verb partly from the participi...
Two branches
用藥讓人安定下來
形容詞說的是「本來就很安定」，動詞說的是「讓他安定下來」。同一個畫面，只是這次有人動手：藥就是那隻把人按下來、讓他坐好的手。這一支跟形容詞來自同一個拉丁動詞，不是另一條來歷。
verb · B2
To give a person or an animal a drug that makes them calm or makes them sleep, usually so that medical treatment can be done.
施打鎮靜劑；使鎮靜