unbeknownst

Từ điển WordNet v3.1 - WordNet Dictionary

I - adjective

(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
• Similar to:
unknown

II - adverb

without someone's knowledge
- unbeknownst to me, she made all the arrangements
• Syn:
unbeknown