lieutenant-colonel; lieutenant colonel(While often written as "Lt. Colonel" in orders and signature blocks, as a courtesy, lieutenant colonels are addressed simply as "colonel" verbally and in the salutation of correspondence. The U.S. Army uses the three letter abbreviation "LTC." The United States Marine Corps and U.S. Air Force use the abbreviations "LtCol" and "Lt Col" (note the space) respectively.); a lieutenant colonel