A preacher usually identifies a person who delivers sermons or homilies on religious topics to an assembly of people, although one can also preach components of any worldview or philosophy. In some traditions a "preacher" is largely synonymous with "evangelist" (the more ancient definition, based on the Greek words underlying the English Bible). Preaching is not limited to religious views, but it extends to moral and social world-views as well.
The word "preach" (from the New Testament Greek κηρύσσω, "to proclaim") usually refers to the proclamation of the gospel of Jesus Christ, i.e. evangelism. Most modern Christians (especially Protestants) also define preaching as a monologue delivered by clergy, normally to laity, that educates the listeners on additional areas of theology more relevant for someone who is already a Christian.
Preachers are common throughout most cultures. They can take the form of a Christian minister on a Sunday morning, or an Islamic Imam. A Muslim preacher in general is referred to as a Da'ee, while those giving sermons on a Friday afternoon are described as a khatib.
The sermon or homily has been an important part of Christian services since Early Christianity, and remains prominent in both Roman Catholicism and Protestantism. Lay preachers sometimes figure in these traditions of worship, for example the Methodist local preachers, but in general preaching has usually been a function of the clergy. The Dominican Order is officially known as the Order of Preachers (Ordo Praedicatorum in Latin); friars of this order were trained to publicly preach in vernacular languages, and the order was created by Saint Dominic to preach to the Cathars of southern France in the early thirteenth century. The Franciscans are another important preaching order; Travelling preachers, usually friars, were an important feature of late medieval Catholicism.
In most denominations, modern preaching is kept below about 40 minutes, but historic preachers of all denominations could at times speak for well over an hour, sometimes for two or three hours, and use techniques of rhetoric and theatre that are today somewhat out of fashion in mainline churches.
In many churches in the United States, the title "Preacher" is synonymous with "Pastor" or "Minister", and the church's minister is often referred to simply as "our/the preacher" or by name such as "Preacher Smith". Sometimes the minister may even be addressed by using the word, such as "Good morning, Preacher".
However, among some Chinese churches, preacher (Chinese:傳道) is different from pastor (Chinese:牧師). A preacher refers to the younger clergy in the Protestant church who are not officially recognised as a pastor until they can prove their capability of leading the church.  for example the holy communion and the baptism.
- Preacher is also the author of the Book of Ecclesiastes according to the King James Version. Preacher is one translation of the Hebrew word קהלת (Qoheleth). There is much debate about the identity of this Preacher; many believe it is Solomon.
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