The Collaborative International Dictionary of English v.0.48:

Preach \Preach\, v. t.
   1. To proclaim by public discourse; to utter in a sermon or a
      formal religious harangue.
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            That Cristes gospel truly wolde preche. --Chaucer.
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            The Lord hath anointed me to preach good tidings
            unto the meek.                        --Isa. lxi. 1.
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   2. To inculcate in public discourse; to urge with earnestness
      by public teaching. "I have preached righteousness in the
      great congregation." --Ps. xl. 9.
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   3. To deliver or pronounce; as, to preach a sermon.
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   4. To teach or instruct by preaching; to inform by preaching.
      [R.] "As ye are preached." --Southey.
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   5. To advise or recommend earnestly.
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            My master preaches patience to him.   --Shak.
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   To preach down, to oppress, or humiliate by preaching.
      --Tennyson.

   To preach up, to exalt by preaching; to preach in support
      of; as, to preach up equality.
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The Collaborative International Dictionary of English v.0.48:

Preach \Preach\, v. i. [imp. & p. p. Preached; p. pr. & vb. n.
   Preaching.] [OE. prechen, OF. preechier, F. pr[^e]cher, fr.
   L. praedicare to cry in public, to proclaim; prae before +
   dicare to make known, dicere to say; or perhaps from
   (assumed) LL. praedictare. See Diction, and cf.
   Predicate, Predict.]
   1. To proclaim or publish tidings; specifically, to proclaim
      the gospel; to discourse publicly on a religious subject,
      or from a text of Scripture; to deliver a sermon.
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            How shall they preach, except they be sent? --Rom.
                                                  x. 15.
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            From that time Jesus began to preach. --Matt. iv.
                                                  17.
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   2. To give serious advice on morals or religion; to discourse
      in the manner of a preacher.
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The Collaborative International Dictionary of English v.0.48:

Preach \Preach\, n. [Cf. F. pr[^e]che, fr. pr[^e]cher. See
   Preach, v.]
   A religious discourse. [Obs.] --Hooker.
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WordNet (r) 3.0 (2006):

preach
    v 1: deliver a sermon; "The minister is not preaching this
         Sunday" [syn: preach, prophesy]
    2: speak, plead, or argue in favor of; "The doctor advocated a
       smoking ban in the entire house" [syn: preach, advocate]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "preach":
   address, admonish, advise, advocate, catechize, caution, charge,
   counsel, deliver a lecture, discourse, encourage, enjoin,
   evangelize, exhort, explain, exposit, expostulate, expound,
   harangue, hold forth, homilize, incite, inculcate, induce,
   issue a caveat, lecture, minister, mission, missionary, moralize,
   move, persuade, point a moral, pontificate, preachify, preaching,
   preachment, prelect, prompt, prophesy, read a lesson,
   read a sermon, remonstrate, reprimand, sermonize, sermonizing,
   speak, talk, urge, warn