Prefix · position · outside
Means "outside" or "external": exotic, exoskeleton, exoplanet, exodus, exosphere.
Written by Bryan López, English teacher · Updated
Exo- comes from Greek "exo" (outside, external) and signals that something is located outside a boundary or comes from the exterior: exoskeleton = skeleton on the outside of the body; exoplanet = planet outside our solar system; exosphere = the outermost layer beyond the atmosphere; exothermic = releasing heat outward. It appears almost exclusively in scientific and academic vocabulary.
Do not confuse exo- (static exterior position) with ex- (movement out of, or "former"): exoskeleton = skeleton positioned on the outside; export = move goods out; exclude = shut out; ex-president = former president. Exo- is Greek and describes position; ex- is Latin and describes movement or past status. In practice, exo- almost always appears in scientific words.
Attaches to scientific nouns to indicate exterior position:
Pronunciation: /ˈeksəʊ/. Do not confuse with ex- (Latin, movement/former): export, exclude, ex-president. Exo- is Greek and describes exterior position; ex- is Latin and describes outward movement or former status.
exo-/ˈeksəʊ/
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"Exo-" (Greek "exo"): static exterior position. "Ex-" (Latin "ex"): outward movement or former status. Exoskeleton = skeleton positioned on the outside. Export = move goods out. Ex-president = former president. Different roots, different uses — though both relate to "outside" in a broad sense.
A trick to remember it
Exo- = outside, external. Almost always scientific: exoskeleton (external skeleton), exoplanet (planet outside our system), exosphere (outer atmosphere), exothermic (releasing heat outward). Pair it with endo- (inside) to understand biology and chemistry vocabulary as contrasting pairs.
Exercise 1 · Form the word
Exercise 2 · Pick the right one
What is the difference between "exo-" and "ex-"?
The prefix exo- means "outside" or "external": exotic, exoskeleton, exoplanet, exodus, exosphere. In Spanish it usually maps to exo-.
The prefix exo- is pronounced /ˈeksəʊ/. For example, "exotic".
"tic" becomes "exotic". It is a typical example of the exo- prefix.
un-, re-, pre-, dis-, over-, in-... every beginning you need to unlock thousands of English words at once.