Definition of "relevancy"

It is the malpractice of the courts to confine evidence and discussion to the bounds of apparent relevancy.

1842, Edgar Allan Poe, The Myster of Marie Rogêt

To believe that such talk really ever came out of people's mouths would be to believe that there was a time when time was of no value to a person who thought he had something to say; when it was the custom to spread a two-minute remark out to ten; when a man's mouth was a rolling-mill, and busied itself all day long in turning four-foot pigs of thought into thirty-foot bars of conversational railroad iron by attenuation; when subjects were seldom faithfully stuck to, but the talk wandered all around and arrived nowhere; when conversations consisted mainly of irrelevancies, with here and there a relevancy, a relevancy with an embarrassed look, as not being able to explain how it got there.

1895, Mark Twain, Fenimore Cooper's Literary Offences