Q. A friend of mine often uses the phrase "split hairs" to mean argue over petty details. Where does this interesting expression come from?

A. We define the phrase "split hairs" as "to make oversubtle or trivial distinctions." As early as 1674, a writer lamented that "the great difficulty so to behave oneself, as to split a hair between them, and never offend either of them." Back then, "split a hair" meant to divide something, as a single strand of hair, evenly so as to give an advantage to no one. To attempt to split something as small as a strand of hair evenly is not only an impossible but also a pointless endeavor. Hence, the phrase soon acquired an ironic reference to arguing over trivialities, and it began to be used disparagingly. Around 1768, an author decried the frustration of petty bickering, asserting "though we are obliged to split the hair, we need not quarter it." To this day, we often use the phrase to convey the futility of wasting time and effort on arguing over something as trivial as how to split a hair evenly.

Q. Could you explain the meaning and origin of "redux"? I have often read of something being "redux," but have never understood the meaning or known the correct pronunciation of the word.

A. The term "redux" is an adjective meaning "brought back." The word, which rhymes with "sea ducks," derives from Latin "reducere," meaning "to lead back," and has been in use since at least 1660. Usually the adjective is placed after the noun it modifies, as in statements like "For a moment it seemed like the same old nightmare - Martina redux, choking up, beating herself." In fact, "redux" can be applied to almost anything from movie heroes to technological projects to politicians.

Until quite recently, this word was used very rarely, though John Dryden and Anthony Trollope had each included it in the title of a work, and it was absent from most dictionaries. But after John Updike used it in 1971 for "Rabbit Redux," the title of the second in his series of novels about Harry "Rabbit" Angstrom, the word caught on, and contemporary dictionaries now routinely include it.

Q. How did the word "mistress" take on its present meaning of a woman who is involved with a married man?

A. The word "mistress," which dates back to the 14th century, is a complex term that conveys a variety of meanings. "Mistress" is the feminine equivalent of "master," and in its oldest, still current sense it denotes a woman who rules or controls, who has others in her employ. From this original meaning emerged a more general sense applied to any proper housewife as the ruler of the household or family. Later, in the early 16th century, "mistress" came to mean "the ruler of a man's heart" and specifically "a sweetheart." From this rather innocent use of the term, the word "mistress" is said to have "declined further to be an only relatively polite term for a woman who illicitly occupies the place of a wife." This sense was common by the 17th century, and it appears in the writings of such authors as Donne, Pope, Byron, and Trollope. In 1859, the historian Macaulay wrote of William Pitt, "His Protestant mistresses gave less scandal than his Popish wife."