English

Definition of unbeknown adjective from the Oxford Advanced Learner's Dictionary

 

unbeknown

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