Source : Webster's Revised Unabridged Dictionary (1913)

Why-not \Why"-not`\, n.
   A violent and peremptory procedure without any assigned
   reason; a sudden conclusive happening. [Obs.]

         When the church Was taken with a why-not in the lurch.
                                                  --Hudibras.

         This game . . . was like to have been lost with a
         why-not.                                 --Nug[ae]
                                                  Antiq.