Merriam-Webster's Word of the Day for June 15, 2024 is:

unbeknownst • \un-bih-NOHNST\  • adjective

Unbeknownst means “without being known about by (a specified person or group of people).”

// Unbeknownst to the students, the teacher had entered the room.

See the entry >

Examples:

“Unbeknownst to many tenants across the city, an obscure city rule requires some newly built rental properties to be put under the city’s rent stabilization ordinance, commonly referred to as rent control.” — Andre Khouri, The Los Angeles Times, 29 Apr. 2024

Did you know?

For reasons unbeknownst to perhaps all of us, unbeknownst is a word in good standing. It has the ring of a true archaism, what with that -st ending we know from such Shakespearean gems as “thou dost snore distinctly,” and yet it is not what it seems; unbeknownst may resemble archaic verb forms like dost and canst, but it’s just playing dress-up. To authentically use dost and canst one has to be addressing someone else, and no one has ever said “thou unbeknownst,” or even “thou beknownst.” Beknown, which had some meager use between the 16th and 19th centuries, was a form of the verb beknow (in use between the 14th and 16th centuries) but was mostly used as an adjective meaning “known, familiar.” If anything would get the -st ending, it would be beknow, and the form would be beknowst or beknowest. All this to say, when unbeknownst started cropping up in fictional dialogue in the early decades of the 19th century, the word did not please everyone. By the early 20th century, it was being disparaged as “a vulgar provincialism” and a term “out of use except in dialect or uneducated speech.” The slander has done no good whatsoever. Unbeknownst is perfectly standard today, even in formal prose. Note that speakers of British English prefer unbeknown, which lacks that unjustified -st and is 200 years older. Perhaps our friends across the pond beknow more than we do.