Definitions for unbeknownˌʌn bɪˈnoʊn; -ˈnoʊnst
Random House Webster's College Dictionary
un•be•knownˌʌn bɪˈnoʊn; -ˈnoʊnst(adj.)
unknown; without one's knowledge (usu. fol. by to).
Origin of unbeknown:
1630–40; un -1+beknown (late ME beknowe, ptp. of beknowen); see be -, known
(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"
without someone's knowledge
"unbeknownst to me, she made all the arrangements"
not known; unknown