A tranquillizer is a drug that calms a person (or an animal) down. For people, it usually means the kind of medicine a doctor gives someone who is very anxious, who cannot stop worrying, or who cannot sleep because their mind is racing. It does not make you happy and it does not cure anything — it turns the feeling down, the way you turn down a radio that is too loud.

A tranquillizer镇定劑 is a drug是一種藥 that calms a person能讓人（or an animal或動物）down冷靜下來。For people對人來說，it usually means它通常是指 the kind of medicine醫生開給 a doctor gives someone非常焦慧的人、who cannot stop worrying一直停不下擔心、or who cannot sleep或是因為 because their mind is racing腦子轉個不停而睡不著的那種藥。It does not make you happy它不會讓你開心，and it does not cure anything也治不好任何病——it turns the feeling down它只是把那種情緒調低，the way you turn down就像你把 a radio that is too loud太吳的收音機 調小聲一樣。

Doctors mostly use more exact words now (like 'sedative', or the names of the actual drug groups), so 'tranquillizer' in everyday English often sounds slightly old-fashioned or vague — it is the word a family uses, not the word on the prescription.

Doctors mostly use more exact words now醫生現在大多用更精確的詞（like 'sedative'像 'sedative'（镇靜劑），or the names of the actual drug groups或直接講藥物類別的名稱），so 'tranquillizer' in everyday English所以 'tranquillizer' 在日常英語裡 often sounds slightly old-fashioned or vague常聽起來有點過時或籠統——it is the word a family uses它是家人之間會用的詞，not the word on the prescription不是處方簻上會寫的詞。

The second common use is for animals: a tranquillizer dart is the dart shot into a big animal to make it sleep so vets can move it or treat it. That use is very much alive, especially in news stories about escaped zoo animals.

The second common use是第二種常見用法 is for animals是用在動物身上：a tranquillizer dart麻醉鶳 is the dart shot into a big animal就是射進大型動物體內的鶳 to make it sleep讓牵睡著 so vets can move it or treat it這樣獸醫才能搬動或治療牵。That use這種用法 is very much alive現在依然很常見，especially in news stories尤其是在新聞報導裡 about escaped zoo animals講動物園動物逃脱的時候。

People also use the word loosely and jokingly for anything that makes them sleepy — 'that lecture was a tranquillizer'.

People also use the word人們也會把這個字 loosely and jokingly拿來輕鬆開玩笑 for anything形容任何 that makes them sleepy讓自己想睡的東西——'that lecture was a tranquillizer'「那堂課根本是镇定劑」。

Spelling: British English writes 'tranquillizer' or 'tranquilliser' with two l's; American English writes 'tranquilizer' with one. All the same word.

Spelling拼法上：British English英式英文 writes 'tranquillizer' or 'tranquilliser'寫成 'tranquillizer' 或 'tranquilliser' with two l's兩個 l；American English美式英文 writes 'tranquilizer'寫成 'tranquilizer' with one只有一個 l。All the same word全部都是同一個字。