Boyd’s Bible Dictionary:

(who exists). (1) Prophet of Judah (1 Kings 16:1-7). (2) Tenth king of Israel B. C. 884-856. He extirpated Ahab’s line according to the prophecies (1 Kings 19:16-17; 2 Kings 9; 10). (3) A Judahite (1 Chron. 2:38). (4) A Simeonite (1 Chron. 4:35). (5) A Benjamite (1 Chron. 12:3).

Concise Bible Dictionary:

1. Son of Jehoshaphat, a son of Nimshi: tenth king of Israel and founder of the fifth dynasty: he reigned from B.C. 884 to 856. Jehu was captain of Jehoram, and was stationed at Ramoth-gilead to keep in check the Syrians on the east of the Jordan. A young man of the prophets, who had been sent by Elisha, arrived at the camp and said he had a message for Jehu. On retiring into the house he anointed Jehu to be king over Israel, with instructions to smite the whole house of Ahab. The prophet opened the door and fled. On Jehu relating what had happened, his companions in arms at once proclaimed him king of Israel (2 Kings 9:1-13).
Jehu lost no time in fulfilling his mission; entering his chariot, he proceeded with some followers in haste to Jezreel, whither king Jehoram, being wounded, had gone to be healed. Jehu and his company were seen by the watchman of the city, and a horseman was despatched to meet him, and to ask if it was peace. Jehu detained him, and likewise a second messenger that was sent. The watchman now discerned that it was Jehu who was in the chariot, by his furious driving. Jehoram and Ahaziah king of Judah (who had come to visit the wounded king) at once each in his own chariot issued forth to meet Jehu. Jehoram, being repulsed by Jehu, called out “Treachery,” and attempted to flee, but an arrow from Jehu pierced his heart and he fell dead. His body was thrown into the field of Naboth the Jezreelite, which Ahab had gained by murder (compare 1 Kings 21:19-29). The king of Judah escaped after being wounded, but died of his wound (2 Kings 9:14-27).
As Jehu entered Jezreel, Jezebel taunted him; but she was thrown down from the window and her body was consumed by dogs, according to the word of the Lord. Jehu then caused the death of seventy of the sons of Jehoram and forty-two of the “brethren of Ahaziah” who came to salute the royal family; and slew all that remained to Ahab, his great men and his priests. Meeting Jehonadab, he took him up in his chariot, saying, “Come with me, and see my zeal for the Lord.” He then in craft gathered together all the priests and worshippers of Baal, for a great sacrifice, completely filling the house of Baal. At his command all were slain, the images burned, and the house destroyed (2 Kings 9:30-10:28).
Jehu was commended for carrying out the will of God in exterminating the house of Ahab, and Jehovah said to him that his children to the fourth generation should sit upon the throne (2 Kings 15:12). But he took no heed to walk in the law of the Lord with all his heart. He did not remove the golden calves, and he departed not from the sins of Jeroboam who made Israel to sin. Therefore God began to cut Israel short by the king of Syria (2 Kings 10:29-36; Hos. 1:4).
The history of Jehu shows how one may have great zeal as far as outward activity goes without a heart set upon serving the Lord.
2. Son of Hanani and a prophet of Judah: he announced the judgment of God against Baasha and rebuked Jehoshaphat (1 Kings 16:1,7,12; 2 Chron. 19:2; 2 Chron. 20:34).
3. Son of Obed, and father of Azariah (1 Chron. 2:38).
4. Son of Josibiah, of the tribe of Simeon (1 Chron. 4:35).
5. An Antothite who joined David at Ziklag (1 Chron. 12:3).

Strong’s Dictionary of Hebrew Words:

from 3068 and 1931; Jehovah (is) He; Jehu, the name of five Israelites
KJV Usage:

Jackson’s Dictionary of Scripture Proper Names:

he shall be (subsist)

Potts’ Bible Proper Names:

The Lord He is; Jehovah is He:―the name of five Israelites [ELIHU], 2 Kings 9:2. {Dominus ille est}