un·less /ənˈlɛs, ˈʌnˌ/
 (conj.)除非除…之外
 Un·less conj.  Upon any less condition than (the fact or thing stated in the sentence or clause which follows); if not; supposing that not; if it be not; were it not that; except; as, we shall fail unless we are industrious.
 Note: ☞ By the omission of the verb in the dependent clause, unless was frequently used prepositionally, -- a construction common in Shakespeare and still employed colloquially.
    Here nothing breeds unless the nightly owl.   --Shak.
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