Use of these terms differs between sects and denominations and even from one community to another. The general term for persons wholly engaged in religious work and set apart from nonprofessional and nonordained worshipers is clergyman. A clergyman may go by the titles of pastor, minister, priest, preacher, parson, cleric, and reverend. It is always safe to refer to such a person as a cleric, clergyman, or man of the cloth (unless the individual is a woman), but choice of other terms depends more upon custom than upon precise meanings of the words involved.
Pastor comes from a Latin word meaning "shepherd" and is specifically applied to one who has the spiritual care of persons entrusted to his charge. Minister, derived from a Latin word meaning "servant," is a somewhat general term that suggests the serving of spiritual needs by one dedicated to that service. Priest, a title largely confined to the Roman Catholic, Anglican, and Eastern Orthodox churches, refers to one whose office it is to perform religious rites of various kinds. The word reverend means "entitled to reverence and respect"; when capitalized it may be prefixed to the name of a clergyman but should always be followed by the title "Mr." or "Dr." or the first name of the individual specified: the "Reverend Mr. Parker" or the "Reverend Roland Parker," not "Reverend Parker."
Dictionary of problem words and expressions. Harry Shaw. 1975.