Prefix · position · inside
Means "inside" or "internal": endoscopy, endocrine, endemic, endorphin, endoskeleton.
Written by Bryan López, English teacher · Updated
Endo- comes from Greek "endon" (within, inside) and signals that something is located inside or originates from within: endoscopy = looking inside the body; endocrine = glands secreting directly into the bloodstream inside; endorphin = a peptide produced inside the brain; endoskeleton = skeleton inside the body; endemic = originating and persisting inside a particular region. It is the direct opposite of exo- (outside).
Endo- is highly productive in scientific vocabulary: endoscope (tool for looking inside), endocrine system (internal hormone regulation), endorphin (internal natural painkiller), endothermic (absorbing heat internally), endogenous (originating from inside an organism), endemic (occurring inside a specific region). The endo-/exo- pairing is one of the most useful prefix pairs in biology and chemistry.
Attaches to scientific nouns to indicate internal position or origin:
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.
endo-/ˈendəʊ/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
"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
Endo- = inside, within. The key pairing to learn: endo- (inside) vs. exo- (outside). Endoskeleton vs. exoskeleton; endothermic vs. exothermic; endogenous vs. exogenous. Once you know this pair, a large section of biology and chemistry vocabulary unlocks instantly.
Exercise 1 · Form the word
Exercise 2 · Pick the right one
What is the difference between "endothermic" and "exothermic"?
The prefix endo- means "inside" or "internal": endoscopy, endocrine, endemic, endorphin, endoskeleton. In Spanish it usually maps to endo-.
The prefix endo- is pronounced /ˈendəʊ/. For example, "endoscopy".
"scopy" becomes "endoscopy". It is a typical example of the endo- prefix.
un-, re-, pre-, dis-, over-, in-... every beginning you need to unlock thousands of English words at once.