Eu - "good," "well," "advantageous," opposite of "Dys"

euphoria

A feeling of great happiness or well-being (ant. Dysphoria)

Euphemism

An indirect, less offensive way of saying something that is considered unpleasant

eupepsia

good digestion (ant. dyspepsia)

euthanasia

mercy killing

euphonious

pleasing in sound (ant. cacophonous)

Eugenics

science dealing with improving hereditary qualities

euthenics

science dealing with improving living conditions

eulogize

write or speak in praise of someone (ant. vilify)