exactly the same as "
unbeknown", but with an "
st" on the end of it, which makes it sound oh-so-much cooler (and much more fun to
pronounce; why else would
they make such a
word? (sort of like
flammable and
inflammable, except that
Webster 1913 defines "flammable" as "inflammable", rather than
the other way around,
which would seem to make more sense)
I would like to point out though, that unbeknown is just "unknown" with a "be" inserted into the middle of it, also for no apparent reason. (it almost makes you wonder if the word "flamble" used to exist.. except that that would be stupid, so of course you wouldn't wonder that!)