I am wondering if you would consider the word hitherto to be outdated. I prefer it over its definition, "until now" and know of no equal alternative. I have been marked down (on papers) for using this "archaic" word. So, is this word outdated? If so, what is a good alternative?
Merriam-Webster Unabridged does not flag hitherto as "archaic."
Macmillan does mark hitherto as "very formal" but it's by no means outdated.
Whoever marked you down for using an "archaic" word is wrong (unless perhaps you were using hitherto in an informal context).
(Disclaimer: I read enough fantasy literature that hitherto seems rather ordinary to me.)
Anecdotally, yes, I would consider it archaic, and if I heard you use it I'd either think you were being pretentious, or that you were deliberately joking about speaking in a pretentious manner.
For reference, I'm a college educated American in my 40s.
As for replacements, I would just use "up to now" or "up till now". "yet" also works in some contexts.
Edit: To further emphasize, despite my education and reasonably broad reading habits, I'm not sure that I could have correctly defined "hitherto" until encountering this question, so this is about more than just trying to avoid seeming old-fashioned. I think using this term outside of certain technical contexts means you will not be widely understood by a general audience.
Though I agree with Gnawme's conclusion, I thought I'd check the Google Ngram viewer to see how "hitherto" compares with "until now" in terms of frequency of usage among their corpus of books in English over the years. The chart shows that the frequency of usage of "hitherto" fell fairly uniformly by 80-90% over the years from 1800 to 2000, with a slight upturn from 2000 to 2008.
Anecdotally, I read/hear the phrase "hitherto unknown" outside of legal or other technical contexts. I wouldn't say it's archaic, but it's not common. You could avoid it in favor of "previous(ly)" when speaking to a large or less-educated audience, but I don't see any reason to drop it from your vocabulary.
To expand on Green Grasso Holm's answer, here are some Ngrams comparing "hitherto", "until now", and "previously". It looks like "hitherto" is relatively more popular in British English, fiction, and phrases.
Extremely formal usage. Many of the answers you received speak to the fact that 60%, 70%, 80%, 90% of the respondents have never heard it used (in spoken language) or have rarely (if ever) seen it used in written form.
Why use a word...when it's probable that 90% of your audience is totally unfamiliar with that word?
Everyone clearly understands what "until now" means.
I would tolerate hitherto, but I would consider the other words from this "set", whitherto and thitherto, to be archaic. Similarly, therefore is fine, but wherefore and especially herefore can sound a bit outdated, though I think they sometimes make more sense in places we use therefore. Just please use therefor correctly.
It is, as Gnawme stated, entirely variable upon the environment in which the word is used or even if it manifests in discourse or written language. For legalese, the Law Dictionary defines hitherto as a 'restrict[ion] [of] the matter in connection with which it is employed to a period of time already passed.'
Therefore, although growing obsolescent in every-day language - Green Grasso presented an 80%-90% decrease between the 1800s and 2000 - it is nevertheless a plenteous lexeme in formal texts!
A similar set of adverbs, 'thereto' and the bygone phrase 'thereunto' might have undertaken a similar trajectory as hitherto, deemed literary or archaic words. This could be extrapolated to hitherto in the future.
'Hitherto' is somewhat archaic, but still used, if largely just in legal writing. It can mean 'up to now', or 'up to a specified time in the past' - i.e. 'up to then'. If the archaic flavour upsets your professor use 'up to now' or 'up to then'. We should always be aware of how what we write will be received by our audience!