In Patrick O'Brian's novel "The Mauritius Command", Captain Jack Aubrey speaks glowingly of the astronomer Caroline Herschel (sister of the more famous astronomer William Herschel), and declares "Ask her the measure of an arc whose cosine is nought, and instantly she replies pi upon two!"
Is this an anchronism? The events of the book take place around 1815, and my Merriam Webster's dictionary (tenth edition) gives 1879 as the first year in which the word "radian" was used. (Clearly Aubrey is referring to the angle-measure of the arc, and not its arc-length, since in the latter case the measure of the arc could not be determined without knowing the radius.)
Earlier in the book, Dr. Stephen Maturin affectionately addresses Aubrey's wife as "Honey" --- a usage of the word I had always associated with twentieth-century America, not nineteenth-century England. But I think it's likely that O'Brian did his homework when choosing the words with which his characters express affection. He might not have been equally careful about the words with which his characters express mathematics!