Prefix · water / hydrogen
Signals relation to water or hydrogen: hydrogen, hydroelectric, hydrocarbon, hydrology.
Written by Bryan López, English teacher · Updated
Hydro- comes from Greek "hydor" (water) and signals a relation to water or to hydrogen (the element that "produces water" when it combines with oxygen). hydroelectric = generates electricity via water; hydroplane = moves over water; dehydrate = lose water; hydrology = the study of the water cycle. Water is the common denominator.
In chemistry, hydro- also signals the presence of hydrogen: hydrogen = the element that "produces water" (hydro + gen = water-producer); hydrocarbon = a compound of hydrogen and carbon (petrol, natural gas, plastics); hydrochloric acid = an acid containing hydrogen and chlorine. In these cases, hydro- signals chemical composition rather than a direct relation to water itself.
Attaches to scientific and technical nouns. Corresponds to Spanish "hidro-":
Pronunciation: /ˈhaɪdrəʊ/. "Hydro" alone informally refers to hydroelectric power in some English-speaking countries. Spanish equivalent: "hidro-."
hydro-/ˈhaɪdrəʊ/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
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.
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
Hydro- = "water" or "hydrogen": hydroelectric = electricity from water, hydrogen = the element that produces water, hydrocarbon = a hydrogen-carbon compound. In English "hydro-"; in Spanish "hidro-." Remember: de-hydrate = remove the water (de- + hydro).
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"?
The prefix hydro- signals relation to water or hydrogen: hydrogen, hydroelectric, hydrocarbon, hydrology. In Spanish it usually maps to hidro-.
The prefix hydro- is pronounced /ˈhaɪdrəʊ/. For example, "hydrogen".
"gen" becomes "hydrogen". It is a typical example of the hydro- prefix.
un-, re-, pre-, dis-, over-, in-... every beginning you need to unlock thousands of English words at once.