by the by

• by the bye, by-the-by, by-the-bye

The second "by" is a noun meaning "a secondary issue". Phrase used since the 17th century.^[1]

by the by

1. Used to introduce a new topic; incidentally, by the way.
   • 1831, L E L[andon], chapter I, in Romance and Reality. , volume II, London: Henry Colburn and Richard Bentley, , →OCLC, pages 70-71:

     Now, Mrs. Clarke was one of those to whom caps and crape were the very morality of mourning—she was not the only one, by the by, with whom propriety stands for principle,...

   • 1892, George Grossmith, Weedon Grossmith, chapter 1, in The Diary of a Nobody:

     She could not get it open, and after all my display, I had to take the Curate (whose name, by-the-by, I did not catch) round the side entrance.

   • 1893, William Morris, The Ideal Book‎:

     Well, I lay it down, first, that a book quite unornamented can look actually and positively beautiful, and not merely un-ugly, if it be, so to say, architecturally good, which, by the by, need not add much to its price […]

   • 2023 January 11, Stephen Roberts, “Bradshaw's Britain: castles and cathedrals”, in RAIL, number 974, page 58:

     By the by, I like Worcester's Shrub Hill station, a three-platform affair of 1850 which may look tired but has character and a splendid frontage on a sunny day.

by the by (comparative more by the by, superlative most by the by)

1. Incidental; unplanned.

   Synonyms: accidental, causeless, random; see also Thesaurus:accidental

   • 1990, Susan Sherman, The color of the heart: writing from struggle & change, 1959-1990:

     These sudden rains. Not tropical - with lightning, thunder, great release after hours of tension. But more nonchalant, more "by-the-by." As if the clouds, rushing to get somewhere else, were to drop some rain in passing.

   • 2008 December 19, Marina Hyde, “Adolf Hitler: My Part in His Downfall, by Tom Cruise”, in The Guardian‎, →ISSN:

     And in the course of interviews on this subject, he is given to denouncing methadone largely on the basis that it was originally called adolphine after Adolf Hitler. That this is an urban myth only peddled by the Church of Scientology is by-the-by.

   • 2019 July 28, Paul MacInnes, “Alexandre Lacazette suffers ankle injury in Arsenal friendly defeat by Lyon”, in The Guardian‎, →ISSN:

     After that, the fact of a Moussa Dembélé double cancelling out Pierre-Emerick Aubameyang’s opener seemed by the by.

• by the way

• “by the by (or bye)”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.