Unless \Un*less"\, conj. [Formerly, onles, onlesse, onlesse
   that, that is, in less, in a less case. See On, and
   Less.]
   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.
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   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.
         [1913 Webster]

               Here nothing breeds unless the nightly owl.
                                                  --Shak.
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