[un.be.knownst] also un.be.known adj [[1]un- + obs. E beknown known; unbeknownst, irreg. fr. unbeknown] (1636): happening without one's knowledge: unknown--usu. used with to
UNBEKNOWNST
Meaning of UNBEKNOWNST in English
Merriam-Webster English vocab. Английский словарь Merriam Webster. 2012