Until this time (2,3)
'until this time' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for hitherto that I've seen before include "Up to this time" , "Up till now" , "So far" , "Previously" , "Heretofore (8" .)
(Other definitions for up to now that I've seen before include "Hitherto" , "So far" .)