[syn: unbeknown, unbeknownst]
The Collaborative International Dictionary of English v.0.48:
Unbeknown \Un`be*known"\, a.
   Not known; unknown. [Colloq.]
   [1913 Webster]
WordNet (r) 3.0 (2006):
unbeknown
    adv 1: without someone's knowledge; "unbeknownst to me, she made
           all the arrangements" [syn: unbeknown, unbeknownst]
    adj 1: (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" [syn:
           unbeknown(p), unbeknownst(p)]
Moby Thesaurus II by Grady Ward, 1.0:
34 Moby Thesaurus words for "unbeknown":
   able, enigmatic, incalculable, incognizable, mysterious, puzzling,
   sealed, strange, unapparent, unapprehended, unascertained,
   uncharted, unclassified, undisclosed, undiscoverable, undiscovered,
   undivulged, unexplained, unexplored, unexposed, unfamiliar,
   unfathomed, unheard, unheard-of, unidentified, uninvestigated,
   unknowable, unknown, unperceived, unplumbed, unrevealed,
   unsuspected, untouched, virgin