“Anachronism: [Stress: “a-NA-kronizm’] In rhetoric, the appearance of a person or thing in the wrong epoch, such as the clock in Shakespeare’s Julius Caesar. Linguistic anachronisms are generally a matter of awareness, context, and expectation: for example, the archaism wight (person, man) may be appropriate at a seminar on the Elizabethan poet Spenser, but is incongruous and probably unintelligible elsewhere. Similarly, a character in a period novel who says OK long before the phrase was current rings false for anyone who knows (or senses) that its time is out of joint.”
Excerpted from: McArthur, Tom. The Oxford Concise Companion to the English Language. New York: Oxford University Press, 2005.