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Fausset's Bible Dictionary [1]

1.  Jeremiah 36:14.

2. ..  Zephaniah 1:1.

3. Joab's retainer, a foreigner, probably from his name a Cushite, and so unrecognized by the watchman, and ignorant of David's devoted affection for Absalom, as appears from the abrupt inconsiderateness with which he announced Absalom's death. Less acquainted also with "the way of the Ciccar," the ground in the Jordan valley, from whence Ahimaaz outran him ( 2 Samuel 18:21-23).

Morrish Bible Dictionary [2]

1. Joab's messenger to David on the death of Absalom.  2 Samuel 18:21-32 , where the R.V. has 'the Cushite.'

2. Ancestor of Jehudi.  Jeremiah 36:14 .

3. Father of Zephaniah the prophet.  Zephaniah 1:1 .

Smith's Bible Dictionary [3]

Cu'shi. Properly, "the Cushite," "the Ethiopian," a man apparently attached to Joab's person.  2 Samuel 18:21-25;  2 Samuel 18:31-32.

Holman Bible Dictionary [4]

 Zephaniah 1:1 2 Jeremiah 36:14

International Standard Bible Encyclopedia [5]

kū´shı̄  : This name represents כּוּשׁי , kūshı̄ , in the original Septuagint Χουσεί , Chouseı́ , Χουσί , Chousı́ ), either with or without the article. With the article (so in  2 Samuel 18:21-32 seven out of eight times, all readings supported by the Septuagint) it simply indicate that the person so designated was of the Cushite people, as in   Jeremiah 38:7 . Its use without the article has doubtless developed out of the foregoing according to a familiar process. For the Cush of Ps 7, title read "Cushi" with Septuagint.

(1) The messenger (the Revised Version (British and American) "the Cushite") sent by Joab to acquaint David with the victory over Absalom. That this man was in fact a foreigner is indicated by his ignorance of a shorter path which Ahimaaz took, by his being unrecognized by the watchman who recognizes Ahimaaz, and by his ignorance, as compared with Ahimaaz, of the sentiments of David, whom he knows only as a king and not as a man.  2 Samuel 18:21 (twice, the second time without the article),   2 Samuel 18:22 ,  2 Samuel 18:23 ,  2 Samuel 18:11 (twice),   2 Samuel 18:32 (twice).

(2) The great-grandfather of Jehudi, a contemporary of Jeremiah ( Jeremiah 36:14 ). The name Jehudi itself ("a man of Judah") is sufficient refutation of the opinion that the use of Cushi as or in lieu of a proper name "seems to show that there were but few Cushites among the Israelites."

(3) The father of Zephaniah the prophet ( Zephaniah 1:1 ).

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [6]

(Heb. Kushi', כּוּשִׁי q. d. Cushite or Ethiopiasn; Sept. Χουσί ; Vulg. Chusi), a name of three men in the Old Test. (See Cush).

1. (With the article, הִכּוּשִׁי , i.e. "the Cushite," "the Ethiopian;" Sept. Χουσί ; Vulg. Chusi .) The messenger sent by Joab to announce to David the success of the battle against Absalom and the death of the young prince ( 2 Samuel 18:21-23;  2 Samuel 18:31-32). B.C. 1023. He was apparently attached to Joab's person, but unknown and unaccustomed to the king, as may be inferred from his not being recognized by the watchman, and also from the abrupt manner in which he breaks his evil tidings to David unlike Ahimaaz, who was well aware of the effect they were sure to produce. (See David). That Cushi was a foreigner as we should infer from his name-is also slightly corroborated by his ignorance of the ground in the Jordan valley "the way of the Ciccar"' (q.v.) by knowing which Ahimaaz was enabled to outrun him. Ewald, however, conjectures that a mode of running is here referred to peculiar to Ahimaaz, and by which he was recognized a long distance off by the watchman.

2. The father of Shelemiah, and great grandfather of Jehudi, which last was sent by the Jewish magnates to invite Baruch to read his roll to them ( Jeremiah 36:14). B.C. long ante 605.

3. The son of Gedaliah, and father of the prophet Zephaniah ( Zephaniah 1:1). B.C. ante 635.