unbeknown
adjective /ˌʌnbɪˈnəʊn/
/ˌʌnbɪˈnəʊn/
(also less frequent unbeknownst
(formal) /ˌʌnbɪˈnəʊnst/
/ˌʌnbɪˈnəʊnst/
)- unbeknown to somebody without the person mentioned knowing
- Unbeknown to her they had organized a surprise party.
Word Originmid 17th cent.: from un- ‘not’ + archaic beknown ‘known’.