Add "unbeknownst"

[getsnoopy]

Not sure why this common word is not part of the dictionary, but it should be.

[Dimitri Papadopoulos Orfanos]

It is part of the en_GB-large and en_US-large dictionaries.

However, depending on your locale, it is part of the smaller en_US dictionary, but not of its UK counterpart en_GB. Doesn't really make sense.

[getsnoopy]

Doesn't really make sense.

Why? It's a word in those locales all the same.

[Dimitri Papadopoulos Orfanos]

That's precisely what doesn't make sense: the word is missing from the en_GB dictionary, but not the en_US or en_CA dictionaries.

[Kevin Atkinson]

To clear up the mystery, unbeknownst is marked a a variant of unbeknown. Oxford has "unbeknownst" marked as a variant of "unbeknown". M-W, instead has this to say (https://www.merriam-webster.com/dictionary/unbeknown):

For reasons unbeknownst to perhaps all of us, unbeknownst is a word in good standing. ... 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.

So I will let both variants in for British English but keep unbeknown marked a a variant for American and Canadian English.