lecturer

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One who delivers lectures, especially professionally.
• noun A member of the faculty of a college or university usually having qualified status without rank or tenure.
• noun A faculty member ranking below an assistant professor.
• noun The academic rank held by such a faculty member.
• noun Chiefly British A university teacher, especially one ranking next below a reader.

from The Century Dictionary.

• noun One who reads or pronounces lectures; a professor or other instructor who delivers formal discourses for the instruction of others.
• noun In the Ch. of Eng., one of a class of preachers not rectors, vicars, or curates, chosen in some parishes by the vestry or chief inhabitants of the parish, with the consent of the incumbent, and supported by voluntary subscriptions and legacies.
• noun In English and American colonial history, a person appointed by municipal or parish authority to deliver a periodical lecture, usually on Sundays or market-days.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who lectures; an assistant preacher.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A person who gives lectures, especially as a profession.
• noun A member of a university or college below the rank of assistant professor or reader.
• noun dated A member of the Church of England clergy whose main task was to deliver sermons (lectures) in the afternoons and evenings.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun someone who lectures professionally
• noun a public lecturer at certain universities