What does "eu" mean? As in EUlogy, EUphony, EUgenics?

see below

The prefix -eu means good, pleasant, or well.

Eulogy is an oral or written piece telling about good or pleasant things about a dead person.

Euphony is a quality that means pleasing to the ear.

Eugenics is the science of breeding human population in order to produce desirable, heritable characteristics.