[adverb] [not gradable] [formal] - until now or until a particular timeThis Saturday sees the first extract from the president's hitherto unpublished diaries.Mira revealed hitherto unsuspected talents on the cricket pitch.When the verdict was announced the prisoner, who had hitherto sat silently throughout the trial, started shouting.
HITHERTO
Meaning of HITHERTO in English
Cambridge English vocab. Кембриджский английский словарь. 2012