late 14c., earlier henne forth (late Old English); see hence + forth.
Entries linking to henceforth
hence adv.
"(away) from here," late 13c., hennes, with adverbial genitive -s + Old English heonan "away, hence," from West Germanic *hin- (source also of Old Saxon hinan, Old High German hinnan, German hinnen), from PIE *ki-, variant of root *ko- "this," the stem of the demonstrative pronoun (see here).
The modern spelling (mid-15c.) is phonetic, to retain the breathy -s- (compare twice, once, since). Original "away from this place;" of time, "from this moment onward," late 14c.; meaning "from this (fact or circumstance)" first recorded 1580s. Wycliffe (1382) uses hennys & þennys for "from here and there, on both sides."
forth adv.
Old English forð "forward, onward, farther; continually;" as a preposition, "during," perfective of fore, from Proto-Germanic *furtha- "forward" (source also of Old Frisian, Old Saxon forth "forward, onward," Old Norse forð, Dutch voort, German fort), from extended form of PIE root *per- (1) "forward." The construction in and so forth was in Old English.