剑桥高阶英汉双解词典 - unbeknown collapse

unbeknown
[UK]/ˌʌn.bɪ'nəʊn/ [US]/-'noʊn/ (also unbeknownst) formal
adverb
unbeknown/unbeknownst to sb
* without a particular person knowing
在（某人）不知道的情况下

1. Unbeknown to me, he'd gone and rented out the apartment in my absence.
他趁我不在的时候走掉了并把公寓租了出去，我根本不知情。

柯林斯COBUILD高阶英汉双解学习词典 - unbeknown collapse

unbeknown
The form unbeknownst /ˌʌnbɪ'nəʊnst/ is also used. 亦使用 unbeknownst.
1.PREP-PHRASE 短语介词在…不知情的情况下；瞒着… If something happens unbeknown to you or unbeknownst to you, you do not know about it.

  • I am appalled that children can mount up debts unbeknown to their parents...

    让我深感震惊的是，孩子们竟会背着父母欠债累累。

  • Unbeknownst to her father, she began taking dancing lessons.

    她瞒着父亲开始去上舞蹈课。

牛津高阶英汉双解 第7版 - unbeknown collapse

unbeknown
un·be·known / 7Qnbi5nEun; NAmE -5noun / (also less frequent un·be·knownst / 7Qnbi5nEunst; NAmE -5nounst / ) adjective    ~ to sb (formal) without the person mentioned knowing
   瞒着；背着:
   Unbeknown to her they had organized a surprise party.
   他们瞒着她筹备了一个给她意外惊喜的聚会。