Tom, "commonly used in tandem with prima" is a bit of an understatement. The
Corpus of Contemporary American English has 230 instances of
facie, and every single one of them is preceded by
prima. It's clear that
prima facie is part of the English language, but I don't think
facie by itself is an English word.
(However,
facies is allowed in Chihuahua - it is a term used with various meanings in biology, medicine and geology. The same word is used for both singular and plural.)
SETI was one of the earliest word suggestions I had to deal with. An anonymous player of
Letterbox proposed it in 2004! I said no then, not because it's an acronym as such, but because it is written in capital letters. I'm happy to allow an acronym like
scuba (originally "self-contained underwater breathing apparatus"), that has morphed into a lower-case spelling, but this doesn't seem to have happened with
SETI. So, sorry, Tom, but it doesn't seem to qualify.