What is the best English translation of
abba (Greek: Αββα, Aramaic: אבא)? What are its senses in the original languages, and are those best captured by
daddy, or something else in English?
Not an expert, but I did have this link sent to me once:
I presume that this in reference to its use in the New Testament. In the Old Testament, it means "father". It's pretty much the only translation for it.
Use in Greek text
Essentially, it's considered more like "daddy" because it's considered more of an "infantile" word that's used. Children called their fathers abba. However, adults used the Greek word pater for "father".