without someone's knowledge; "unbeknownst to me, she made
all the arrangements" Synonym(s):unbeknown, unbeknownst
adj
(usually used with `to') occurring or existing without
the knowledge of; "a crisis unbeknown to me"; "she had been ill for months, unbeknownst to the family" Synonym(s):unbeknown(p), unbeknownst(p)
From Webster's Revised Unabridged Dictionary (1913) [web1913]:
Unbeknown \Un`be*known"\, a.
Not known; unknown. [Colloq.]