What does the prefix hydro- mean?
Hydro- comes from the Greek hydor, which means "water". It shows a relation to water or to its movement. You will find it in words about energy, health and chemistry.
ESEN
Prefix · water / hydrogen
hydro-
Signals relation to water or hydrogen: hydrogen, hydroelectric, hydrocarbon, hydrology.
Scientific
Written by Bryan López, English teacher · Updated
Hydro- in chemistry: hydrogen
In chemistry, hydro- also shows the presence of hydrogen, the element whose name literally means "the one that produces water" when it combines with oxygen. In those cases, hydro- no longer talks about the water you drink, but about the chemical makeup of a substance. So when you see a word with hydro-, ask yourself: is it about water, or about hydrogen?
How it is used
Attaches to scientific and technical nouns:
- hydro- + field/process (water)electric → hydroelectricplane → hydroplanetherapy → hydrotherapylogy → hydrology
- hydro- + chemical compoundgen → hydrogencarbon → hydrocarbonchloric → hydrochloricphobia → hydrophobia
Pronunciation: /ˈhaɪdrəʊ/. "Hydro" alone informally refers to hydroelectric power in some English-speaking countries.
How it is pronounced
hydro-/ˈhaɪdrəʊ/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
Examples
Root word
With hydro-
In a phrase
- genhydrogenHydrogen is the lightest and most abundant element in the universe.
- electrichydroelectricThe dam generates hydroelectric power from the river's flow.
- carbonhydrocarbonNatural gas and petrol are both types of hydrocarbon.
- logyhydrologyHydrology studies how water moves through rivers and aquifers.
- phobiahydrophobiaHydrophobic surfaces repel water, which is useful in waterproof coatings.
- therapyhydrotherapyHydrotherapy is recommended for patients recovering from joint surgery.
- chlorichydrochloricHydrochloric acid is produced in the stomach to help digest food.
Common mistakes
hydrogen is called that because it was found in water
hydrogen was named because burning it produces water (hydro = water, gen = that which produces)
Hydrogen was named by Lavoisier in 1783. When hydrogen burns, it combines with oxygen to produce water (H₂O). Hydro- (water) + gen (from Greek "genos" = producer) = the element that produces water.
hydrophobia = only the medical fear of water
hydrophobia also means rabies (historically) and in chemistry means water-repelling
Historically, "hydrophobia" was the term for rabies (the disease causes a horror of water). In chemistry, "hydrophobic" = water-repelling (like oil or wax). "Hydrophilic" = water-attracting. The context determines the meaning.
A trick to remember it
Think of hydration, giving your body water: hydro- = water. hydration, hydroelectric.
Practise what you learned
Exercise 1 · Form the word
Exercise 2 · Pick the right one
"Natural gas and petrol are both forms of ___, compounds made only of hydrogen and carbon."
Exercise 3 · Pick the right one
Why is hydrogen called "hydrogen"?
Frequently asked questions
What does the prefix hydro- mean in English?
The prefix hydro- signals relation to water or hydrogen: hydrogen, hydroelectric, hydrocarbon, hydrology.
How do you pronounce hydro-?
The prefix hydro- is pronounced /ˈhaɪdrəʊ/. For example, "hydrogen".
Can you give an example of a word with hydro-?
"gen" becomes "hydrogen". It is a typical example of the hydro- prefix.
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