What is the Greek word for godson?

There isn't a single, direct Greek word for "godson." The concept is expressed using a phrase that describes the relationship. For example, you might use a phrase incorporating words like ἀνηψιός (anēpsiós, nephew), ἀδελφός (adelphós, brother), or a descriptive phrase involving the godfather's role and the relationship to the child, depending on the context. The specific phrase would depend on whether the godparent is male or female and their relationship to the child's parents.