ˈtha(a)]r]d.əˌfō(ə)r, ˈthe], ]ə], ]tə, -fȯ(ə)r, -fōə, -fȯ(ə), ˌ ̷ ̷ ̷ ̷ˈ ̷ ̷ adverb
Etymology: Middle English ther tofore, from ther there + tofore before — more at heretofore
: up to that time : until then : before then
theretofore obscure community — Robert Rice
new knowledge produced powerful techniques for smashing the theretofore indestructible atom — Barry Commoner