Definition from Wiktionary, the free dictionary
unbeknownst (not comparable)
- (followed by to) without the knowledge of
- He went home early, unbeknownst to his mother.
Some writers advise against using this word, describing it as "unnecessary". It is true that it can usually be replaced by unknown (to), though the sentence may need rearranging to sound natural.
- Unknown to his mother, he went home early.
Without the knowledge of