It's Merriam-Webster's Word of the Day for June 15th.
Today's word is unbeknownst, spelled U-N-B-E-K-N-O-W-N-S-T.
Unbeknownst is an adjective.
It means without being known about by a specified person or group of people.
Here's the word used in a sentence from the LA Times.
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.
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 Canced.
But it's just playing dress-up.
To authentically use Dost and Canced, 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 be-know.
in use between the 14th and 16th centuries,
but was mostly used as an adjective, meaning known or familiar.