Hitherto means up until this point in time. Hitherto unknown, hitherto unpublished, hitherto it had worked.
It is formal and implies that things are about to change, which is why hitherto unknown is such a common phrase in announcements. The hither in it is the old word for to this place.
1adverbhithertoUp until this point in time.
“The village, hitherto quiet and forgotten, was suddenly full of tourists.”
hitherto is a time.
Middle English hiderto is hither, to this place, plus to.
Proto-Indo-European
*ḱe
Old English
hider — to here, hither
Middle English
hiderto — to the present time, until now; up to this point
English, today
hitherto
Built from
The is derived from Middle English hiderto (“to the present time, until now; up to this point”), from hider (“in this direction, to or toward this place; up to the present time, until now”) (from Old English hider (“to here, hither”)) + to (“in the direction of, toward; etc.”). by surface analysis, hither + to. The is derived from the adverb.
Etymology from Wiktionary, CC BY-SA