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Turbidity is how cloudy or muddy a liquid is — how much tiny stuff is floating in it so you cannot see through. Clear water has low turbidity. Water after a typhoon, full of mud and sand, has high turbidity. The important thing is that the stuff is *floating*, not sitting at the bottom; once it settles, the water gets clear again and the turbidity drops. This is a measuring word, so it is mostly used by scientists, water companies, and people who test rivers and fish tanks. They give it a number with a machine that shines light through the water: the more light gets blocked, the higher the number. Normal people do not say this word; they say 'the water is cloudy' or 'the water is dirty'. You will meet 'turbidity' in a news report about tap water after heavy rain, in a science class, or on a report about a reservoir. The adjective 'turbid' is even rarer in speech — writers sometimes use it for a river, and sometimes, in a book-ish way, for feelings or thoughts that are confused and , though actually that use sounds old-fashioned now.
濁度（水的混濁程度，自來水公司和環境檢測常用的正式量測詞）
組成turbid（混濁的）+ -ity（把形容詞變成名詞，指「那個性質」）。turbid 來自拉丁文 turbidus，跟「攪動、弄亂」有關 —— 水被攪動，泥沙浮起來，就變濁了。
同家族的字
- turbidthe adjective this noun is built from: cloudy with floating dirt
- disturbboth go back to Latin turba/turbare, to stir up and throw into disorder — disturbing water is literally what makes it turbid
- turbulencesame Latin root of stirring and violent movement; the shaky air a plane hits
原始詞典資料2 筆記錄
以下是外部詞典記錄的用法，原文照列，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。
turbiditynoun
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The state of being turbid; turbidness.
- The variables we considered include solar irradiance and turbidity, which are relevant to the symbiont photosynthesis and yearly minimum temperature, representing potential limiting factors for the holobiont.
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The measure of transparency of a fluid (units of measurement include Nephelometric Turbidity Unit (NTU)).
- Over a 5 days period beginning on November 21, 2011 and ending on November 26, 2011 we deployed an array of hydrodynamic and sediment dynamic sensors on a tripod frame, including two turbidity sensors, two pore water pressure sensors, one sea gauge wave tide recorder, one kinemometer, and one acoustic erosion measuring instrument (Fig. 21.2).
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。