|Easton's Bible Dictionary|
(1.) One of the chiefs who subscribed the covenant (Nehemiah 10:21).
(2.) The last high priest mentioned in the Old Testament (Nehemiah 12:11, 22), sons of Jonathan.
Int. Standard Bible Encyclopedia
jad'-u-a, ja-du'-a (yaddua`, "known"):
(1) One of the "chiefs of the people" who with Nehemiah sealed the covenant, thus signifying their voluntary acceptance of the law and their solemn promise to submit to its yoke (Nehemiah 10:21 (Hebrew 22)).
(2) Son of Jonathan or Johanan, and great-grandson of Eliashib, the high priest in Nehemiah's time (Nehemiah 12:11, 22). He is the last of the high priests mentioned in the Old Testament, and held office during the reign of Darius the Persian, i.e. Darius III Codomannus, the last king of Persia (336-332 B.C.), who was overthrown by Alexander the Great. It is doubtless to him that Josephus refers in his romantic account of Alexander's entrance into Jerusalem (Ant., XI, viii, 4; vii, 2; viii, 7).
Jaddua (3 Occurrences)
Nehemiah 10:21 Meshezabel, Zadok, Jaddua, (WEB KJV JPS ASV BBE DBY WBS YLT NAS NIV)
Nehemiah 12:11 and Joiada became the father of Jonathan, and Jonathan became the father of Jaddua. (WEB KJV JPS ASV BBE DBY WBS YLT NAS NIV)
Nehemiah 12:22 As for the Levites, in the days of Eliashib, Joiada, and Johanan, and Jaddua, there were recorded the heads of fathers' houses; also the priests, in the reign of Darius the Persian. (WEB KJV JPS ASV BBE DBY WBS YLT NAS NIV)