What does the prefix endo- mean?
Endo- comes from the Greek endon, which means "within". It shows that something is inside or comes from the inside. It is the opposite of exo-, which means "outside".
ESEN
Prefix · position · inside
endo-
Means "inside" or "internal": endoscopy, endocrine, endemic, endorphin, endoskeleton.
Scientific
Written by Bryan López, English teacher · Updated
Endo- in medicine and biology
Endo- appears mostly in medicine and biology, always to talk about what happens, is produced or is studied inside the body or a region. That makes it a useful prefix for understanding health news and scientific texts. If you see endo- in a word, think: "from the inside".
How it is used
Attaches to scientific nouns to indicate internal position or origin:
- endo- + scientific nounscope → endoscopecrine → endocrineskeleton → endoskeletonthermic → endothermic
- common formsrphin → endorphinmic → endemicgenous → endogenousmetrium → endometrium
Pronunciation: /ˈendəʊ/. The key pairing: endo- (inside) vs. exo- (outside). Endoskeleton vs. exoskeleton; endothermic vs. exothermic; endogenous vs. exogenous. Learning these pairs doubles vocabulary acquisition efficiency.
How it is pronounced
endo-/ˈendəʊ/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
Examples
Root word
With endo-
In a phrase
- scopyendoscopyThe doctor recommended an endoscopy to examine her stomach lining.
- crineendocrineThe endocrine system regulates hormones throughout the entire body.
- micendemicMalaria is endemic to many tropical regions of the world.
- rphinendorphinExercise triggers endorphins, which naturally reduce pain and boost mood.
- skeletonendoskeletonHumans have an endoskeleton made of bones inside the body.
- thermicendothermicPhotosynthesis is an endothermic process that absorbs energy from sunlight.
- genousendogenousMany diseases have endogenous causes that originate inside the body itself.
Common mistakes
endo- and en-/em- are the same prefix
endo- (Greek, interior position, scientific vocabulary) and en-/em- (Latin/Old English, causative "make") are different in origin and use
"Endo-" (Greek "endon"): interior position. Endoscopy = examining the inside. "En-/em-" (Latin/Old English): causative. Enable = make able; enrich = make rich. The initial "en-" sound can cause confusion, but endo- is always Greek and scientific; en- is causative and general. Context usually makes the distinction clear.
A trick to remember it
The opposite of exo- (which you already saw): endo- = inside. endoscopy, endocrine.
Practise what you learned
Exercise 1 · Form the word
Exercise 2 · Pick the right one
What is the difference between "endothermic" and "exothermic"?
Frequently asked questions
What does the prefix endo- mean in English?
The prefix endo- means "inside" or "internal": endoscopy, endocrine, endemic, endorphin, endoskeleton.
How do you pronounce endo-?
The prefix endo- is pronounced /ˈendəʊ/. For example, "endoscopy".
Can you give an example of a word with endo-?
"scopy" becomes "endoscopy". It is a typical example of the endo- prefix.
Other useful prefixes
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