Is it ensure, insure, or assure?
late 12c., "person who speaks for God; one who foretells, inspired preacher," from Old French prophete, profete "prophet, soothsayer" (11c., Modern French prophète) and directly from Latin propheta, from Greek prophetes (Doric prophatas) "an interpreter, spokesman," especially of the gods, "inspired preacher or teacher," from pro- "before" (see pro-) + root of phanai "to speak," from PIE *bha- (2) "speak" (see fame (n.)).
The Greek word was used in Septuagint for Hebrew nabj "soothsayer." Early Latin writers translated Greek prophetes with Latin vates, but the Latinized form propheta predominated in post-Classical times, chiefly due to Christian writers, probably because of pagan associations of vates. In English, meaning "prophetic writer of the Old Testament" is from late 14c. Non-religious sense is from 1848; used of Muhammad from 1610s (translating Arabic al-nabiy, and sometimes also al-rasul, properly "the messenger"). The Latin word is glossed in Old English by witga.
Someone who brings a message from God to people. The best-known prophets are those of the Old Testament. Their most frequent themes were true worship of God, upright living, and the coming of the Messiah. They often met with bitter resistance when they spoke against the idol worship and immorality of their people. Among the prophets of the Old Testament were Daniel, Elijah, Isaiah, Jeremiah, Jonah, and Moses.
Prophets also appear in the New Testament. Jesus called John the Baptist a prophet; Christians consider him a bridge between the prophets of the Old Testament and those of the New Testament. Jesus mentions “true prophets” and “false prophets” — those who present the true message of God and those who present a counterfeit (see By their fruits ye shall know them and wolves in sheep's clothing). He himself was considered a prophet in his lifetime (see A prophet is not without honor save in his own country) and is still widely revered by non-Christians as a prophet, though not as the Messiah. The New Testament also mentions that some of the early Christians were prophets who spoke inspired messages to their communities.
Note: In general usage, a “prophet” is someone who can foretell the future. The prophets of the Bible often made predictions, which confirmed their authority when the predictions came true, but changing the lives of their people was a more central part of their mission.
(Heb. nabi, from a root meaning "to bubble forth, as from a fountain," hence "to utter", comp. Ps. 45:1). This Hebrew word is the first and the most generally used for a prophet. In the time of Samuel another word, _ro'eh_, "seer", began to be used (1 Sam. 9:9). It occurs seven times in reference to Samuel. Afterwards another word, _hozeh_, "seer" (2 Sam. 24:11), was employed. In 1 Ch. 29:29 all these three words are used: "Samuel the seer (ro'eh), Nathan the prophet (nabi'), Gad the seer" (hozeh). In Josh. 13:22 Balaam is called (Heb.) a _kosem_ "diviner," a word used only of a false prophet. The "prophet" proclaimed the message given to him, as the "seer" beheld the vision of God. (See Num. 12:6, 8.) Thus a prophet was a spokesman for God; he spake in God's name and by his authority (Ex. 7:1). He is the mouth by which God speaks to men (Jer. 1:9; Isa. 51:16), and hence what the prophet says is not of man but of God (2 Pet. 1:20, 21; comp. Heb. 3:7; Acts 4:25; 28:25). Prophets were the immediate organs of God for the communication of his mind and will to men (Deut. 18:18, 19). The whole Word of God may in this general sense be spoken of as prophetic, inasmuch as it was written by men who received the revelation they communicated from God, no matter what its nature might be. The foretelling of future events was not a necessary but only an incidental part of the prophetic office. The great task assigned to the prophets whom God raised up among the people was "to correct moral and religious abuses, to proclaim the great moral and religious truths which are connected with the character of God, and which lie at the foundation of his government." Any one being a spokesman for God to man might thus be called a prophet. Thus Enoch, Abraham, and the patriarchs, as bearers of God's message (Gen. 20:7; Ex. 7:1; Ps. 105:15), as also Moses (Deut. 18:15; 34:10; Hos. 12:13), are ranked among the prophets. The seventy elders of Israel (Num. 11:16-29), "when the spirit rested upon them, prophesied;" Asaph and Jeduthun "prophesied with a harp" (1 Chr. 25:3). Miriam and Deborah were prophetesses (Ex. 15:20; Judg. 4:4). The title thus has a general application to all who have messages from God to men. But while the prophetic gift was thus exercised from the beginning, the prophetical order as such began with Samuel. Colleges, "schools of the prophets", were instituted for the training of prophets, who were constituted, a distinct order (1 Sam. 19:18-24; 2 Kings 2:3, 15; 4:38), which continued to the close of the Old Testament. Such "schools" were established at Ramah, Bethel, Gilgal, Gibeah, and Jericho. The "sons" or "disciples" of the prophets were young men (2 Kings 5:22; 9:1, 4) who lived together at these different "schools" (4:38-41). These young men were taught not only the rudiments of secular knowledge, but they were brought up to exercise the office of prophet, "to preach pure morality and the heart-felt worship of Jehovah, and to act along and co-ordinately with the priesthood and monarchy in guiding the state aright and checking all attempts at illegality and tyranny." In New Testament times the prophetical office was continued. Our Lord is frequently spoken of as a prophet (Luke 13:33; 24:19). He was and is the great Prophet of the Church. There was also in the Church a distinct order of prophets (1 Cor. 12:28; Eph. 2:20; 3:5), who made new revelations from God. They differed from the "teacher," whose office it was to impart truths already revealed. Of the Old Testament prophets there are sixteen, whose prophecies form part of the inspired canon. These are divided into four groups: (1.) The prophets of the northern kingdom (Israel), viz., Hosea, Amos, Joel, Jonah. (2.) The prophets of Judah, viz., Isaiah, Jeremiah, Obadiah, Micah, Nahum, Habakkuk, Zephaniah. (3.) The prophets of Captivity, viz., Ezekiel and Daniel. (4.) The prophets of the Restoration, viz., Haggai, Zechariah, and Malachi.