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Prefix · good / well / normal

eu-

Signals something good, normal, or favorable: euphoria, euthanasia, eulogy, euphemism.

Literary

Written by Bryan López, English teacher · Updated October 2026

What does eu- mean in English?

Eu- comes from the Greek eu, which means "well" or "good". It shows something favorable or that works as it should. It is the exact opposite of dys-, which means "bad" or "difficult". If you see eu- at the start of a word, think of something good, correct or pleasant.

Eu- in biology and philosophy

In biology, eu- can also mean "true", as in cells with a well-formed nucleus. In philosophy it appears in Aristotle's idea of human flourishing: living well, in the deepest sense. It is a rare prefix in everyday conversation, but it shows up in academic and scientific readings in English.

How it is used

Attaches to philosophical, medical, and scientific nouns:

eu- + state/emotion
phoria → euphoriathymia → euthymiaphony → euphonygenic → eugenic
eu- + scientific/philosophical term
karyote → eukaryotethanasia → euthanasialogy → eulogydaimonia → eudaimonia

Pronunciation: /juː/. The exact antonym of dys- (bad, difficult).

How it is pronounced

eu-/juː/

Tap the button to hear how the prefix sounds. Each word in the table has its own audio.

Examples

Root word

With eu-

In a phrase

phoriaeuphoriaThe athlete felt pure euphoria crossing the finish line after four years of training.
thanasiaeuthanasiaThe euthanasia debate balances a patient's right to choose with a doctor's duty of care.
logyeulogyHer son delivered a moving eulogy that left the congregation in tears.
phonyeuphonyThe poem's euphony makes it very pleasant to read aloud.
karyoteeukaryoteHuman cells are eukaryotes, each with a nucleus holding the genetic material.
phemismeuphemism"Collateral damage" is a euphemism for civilian deaths in armed conflict.

Common mistakes

euthanasia = assisted suicide

euthanasia = the deliberate ending of a patient's life to relieve suffering, administered by a physician; distinct from assisted suicide

"Euthanasia" (from Greek "eu" = good + "thanatos" = death) = good death. In medical ethics: "euthanasia" = the physician administers the lethal treatment directly. "Assisted suicide" = the physician provides the means (a prescription) but the patient takes the final action themselves. They are legally and ethically distinct in most frameworks.

euphemism = a metaphor or rhetorical figure

euphemism = the substitution of a mild or indirect expression for a harsh, blunt, or taboo one

"Euphemism" (eu- = well + pheme = speech) = good/gentle speech. Examples: "pass away" for "die"; "let go" for "fired"; "collateral damage" for "civilian casualties." A euphemism is a communication strategy — replacing harsh directness with softer language — rather than a rhetorical figure like metaphor.

A trick to remember it

Think of "euphoric" (feeling great): eu- = good, favorable. euphoria, eulogy.

Practise what you learned

Exercise 1 · Form the word

Exercise 2 · Pick the right one

"The politician used 'collateral damage' as a ___, avoiding the more direct phrase 'civilian deaths.'"

Exercise 3 · Pick the right one

What is the precise difference between "euthanasia" and "assisted suicide" in medical ethics?

Frequently asked questions

What does the prefix eu- mean in English?

The prefix eu- signals something good, normal, or favorable: euphoria, euthanasia, eulogy, euphemism.

How do you pronounce eu-?

The prefix eu- is pronounced /juː/. For example, "euphoria".

Can you give an example of a word with eu-?

"phoria" becomes "euphoria". It is a typical example of the eu- prefix.

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