by the by

Bye \Bye\ (b[imac]), n.
   1. A thing not directly aimed at; something which is a
      secondary object of regard; an object by the way, etc.; as
      in on or upon the bye, i. e., in passing; indirectly; by
      implication. [Obs. except in the phrase by the bye.]
      [1913 Webster]

            The Synod of Dort condemneth upon the bye even the
            discipline of the Church of England.  --Fuller.
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   2. (Cricket) A run made upon a missed ball; as, to steal a
      bye. --T. Hughes.
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   3. In various sports in which the contestants are drawn in
      pairs, the position or turn of one left with no opponent
      in consequence of an odd number being engaged; as, to draw
      a bye in a round of a tennis tournament.
      [Webster 1913 Suppl.]

   4. (Golf) The hole or holes of a stipulated course remaining
      unplayed at the end of a match.
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   {By the bye}, in passing; by way of digression; apropos to
      the matter in hand. [Written also {by the by}.]
      [1913 Webster]