Common words:
* eulogy: a speech praising someone who has died
* euphoria: a feeling of intense happiness and excitement
* euphemism: a mild or indirect word or expression substituted for one considered to be too harsh or blunt
* euphony: pleasant or harmonious sound
Less common words:
* eukaryote: an organism whose cells have a nucleus enclosed within a membrane
* eupepsia: good digestion
* eugenic: relating to the improvement of the human race by controlled breeding
* euthanasia: the painless killing of a patient suffering from an incurable and painful disease or illness
* euthenics: the science of improving human living conditions
* eupnea: normal, quiet breathing
* eutaxia: good order or arrangement
* eudaimonia: a state of well-being and fulfillment
* eustress: a positive stress that is beneficial and motivating
Note: The prefix "eu-" generally indicates something good, pleasant, or easy.