by the way

• BTW, btw (initialism)

First appeared in the 10th century with literal meaning "by the side of the road", from Old English weġ (which became "way") meaning "road". Soon afterward (circa 1000) it came to mean "during one's journey". The figurative meaning developed in the mid-16th century, with the first instance of the modern meaning being from 1614.^[1]

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by the way

1. (conjunctive, idiomatic) Incidentally; used in referencing a parenthetical statement not timely, central, or crucial to the topic at hand; foregone, passed by, something that has already happened.

   Synonyms: apropos, BTW, by the by, incidentally

   His mother will be coming for dinner tomorrow, and, by the way, she recently sold her collection of ceramic eggs.

   • 1853, Herman Melville, Bartleby, the Scrivener, in Billy Budd, Sailor and Other Stories, New York: Penguin Books, 1968; reprint 1995 as Bartleby, ISBN 0 14 60.0012 9, p.2:

     I had counted on a life-lease of the profits, whereas I only received those of a few short years. But this is by the way.

   • 1918, W B Maxwell, chapter VII, in The Mirror and the Lamp, Indianapolis, Ind.: The Bobbs-Merrill Company, →OCLC:

     “A very welcome, kind, useful present, that means to the parish. By the way, Hopkins, let this go no further. We don't want the tale running round that a rich person has arrived. Churchill, my dear fellow, we have such greedy sharks, and wolves in lamb's clothing. […]”

by the way (not comparable)

1. (UK, idiomatic) Irrelevantly, off-topic.(Can we add an example for this sense?)