🔼The name Jaddai or Jadau in the Bible
The name Jaddai is a bit mysterious, and that's because, technically, it doesn't really occur in the Bible.
In Ezra 10:43, a son of Nebo called ידו (Jadau; highly similar to the name Iddo) is mentioned among the men who married and divorced their foreign wives. But in the Kethib & Qere — which is a reading system related to the Masoretic effort to preserve proper pronunciation — this name is spelled ידי (Jaddai).
Modern translations such as the NAS, NIV, Darby and the revised King James speak of Jaddai in this verse, but older translations, such as the original King James, Green and Webster (both original and revised) speak of Jadau. The ASV translation has Iddo.
🔼Etymology and meaning of the name Jaddai, Jadau
For a meaning, there are several ways to go with this name.
BDB Theological Dictionary doesn't translate our name but lists it under the root דוד (dwd), the assumed root for words that have to do with love:
Alfred Jones (Dictionary of Old Testament Proper Names) concurs with BDB and reads Beloved Of The Lord.
The problem is that these roots and all their derivatives are spelled with a double letter ד (daleth), while the names Jaddai and Jadau are spelled with just one. Perhaps linguistically the two are related, but in practice, few Hebrew readers would recognize that association.
NOBSE Study Bible Name List avoids the problem of the double d, and goes with the root ידה (yada), meaning to praise or confess:
Hence for a meaning of the name Jaddai, NOBSE reads Praised.