Easton's Bible Dictionary (1897)
In the Old Testament the Hebrew word tsir, meaning “one who goes on an errand,” is rendered thus (Josh. 9:4; Prov. 13:17; Isa. 18:2; Jer. 49:14; Obad. 1:1). This is also the rendering of melits, meaning “an interpreter,” in 2 Chr. 32:31; and of malak, a “messenger,” in 2 Chr. 35:21; Isa. 30:4; 33:7; Ezek. 17:15. This is the name used by the apostle as designating those who are appointed by God to declare his will (2 Cor. 5:20; Eph. 6:20).
, to contract alliances (Josh. 9:4), to solicit favours (Num. 20:14), to remonstrate when wrong was done (Judg. 11:12), to condole with a young king on the death of his father (2 Sam. 10:2), and to congratulate a king on his accession to the throne (1 Kings 5:1). To do injury to an ambassador was to insult the king who sent him (2 Sam. 10:5).
Smith's Bible Dictionary (1863)
a person of high rank employed by a government to represent it and transact its business at the seat of government of some other power.
The earliest examples of ambassadors employed occur in (Numbers 20:14; 21:21; Judges 11:7-19) afterwards in that of the fraudulent Gibeonites, (Joshua 9:4) etc., and in the instances of civic strife mentioned (Judges 11:12) and Judg 20:12 Ambassadors are found to have been employed not only on occasions of hostile challenge or insolent menace, (1 Kings 20:2,6; 2 Kings 14:8) but of friendly compliment, of request for alliance or other aid, of submissive deprecation and of curious inquiry. (2 Kings 14:8; 16:7; 18:14; 2 Chronicles 32:31) Ministers are called ambassadors of Christ.
Hastings' Dictionary of the Bible (1898) & Schaff's Bible Dictionary
AMBAS'SADOR, a person of the highest rank, appointed to represent his government in the transaction of business with a foreign power. The earliest mention in the Bible is in the case of the Edomites, Num 20:14, to whom Moses sent "messengers," also in the case of Moab, the Amorites, the Gibeonites, and other tribes. See Num 21:21;Josh 9:4; Jud 11:17-19. In the days of the kingdoms they are more frequently mentioned. An injury upon them was an insult to their king. 2 Sam 10:5. Their mission was often pacific or congratulatory, as in the latter incident.
Paul calls gospel-preachers the ambassadors of Christ. 2 Cor 5:20.