The term 'hitherto unknown' refers to something that has not been seen or experienced before. The crossword solutions for this term are 'NEW, ' 'STRANGE, ' and 'NOVEL.' These words all describe something that is unfamiliar and has not been encountered before. NEW implies something that has recently come into existence, while STRANGE suggests something that is unfamiliar and out of the ordinary. NOVEL implies something that is unique and original. All three words can be used to describe something that is hitherto unknown.