The Collaborative International Dictionary of English v.0.48:

Prophet \Proph"et\, n. [F. proph[`e]te, L. propheta, fr. Gr. ?,
   literally, one who speaks for another, especially, one who
   speaks for a god an interprets his will to man, fr. ? to say
   beforehand; ? for, before + ? to say or speak. See Fame. ]
   [1913 Webster]
   1. One who prophesies, or foretells events; a predicter; a
      foreteller.
      [1913 Webster]

   2. One inspired or instructed by God to speak in his name, or
      announce future events, as, Moses, Elijah, etc.
      [1913 Webster]

   3. An interpreter; a spokesman. [R.] --Ex. vii. 1.
      [1913 Webster]

   4. (Zool.) A mantis.
      [1913 Webster]

   School of the prophets (Anc. Jewish Hist.), a school or
      college in which young men were educated and trained for
      public teachers or members of the prophetic order. These
      students were called sons of the prophets.
      [1913 Webster]

WordNet (r) 3.0 (2006):

prophet
    n 1: an authoritative person who divines the future [syn:
         prophet, prophesier, oracle, seer, vaticinator]
    2: someone who speaks by divine inspiration; someone who is an
       interpreter of the will of God

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "prophet":
   Cassandra, Don Quixote, Druid, Quixote, astrologer, augur,
   calamity howler, clairvoyant, crystal gazer, daydreamer, divinator,
   diviner, divineress, dreamer, dreamer of dreams, enthusiast,
   escapist, forecaster, foreknower, foreseer, foreshower, foreteller,
   fortune-teller, fortuneteller, geomancer, haruspex, idealist,
   lotus-eater, oracle, palmist, predictor, prefigurer, presager,
   prognosticator, prophesier, prophet of doom, prophetess, psychic,
   pythoness, religious prophets, rhapsodist, romancer, romantic,
   romanticist, seer, seeress, sibyl, soothsayer, utopian, utopianist,
   utopianizer, vates, visionary, warlock, weather prophet,
   wishful thinker, witch



Easton's 1897 Bible Dictionary:

Prophet
   (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.