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Death Match
In modern Japanese, 真剣勝負 means to take something very seriously.
The literal and historical meaning is “real sword battle.” In old times, a Samurai apprentice would practice with a wooden practice sword. Once trained and qualified, they would wield a real steel sword made for battle and killing. They were ready for a “death match” or Shinken Shobu.
真剣 is an adjective that has come to mean serious/earnest. The literal translation is “real sword.”
勝負 in the simplest terms, means match, contest, game, or bout. Depending on the context, it could also mean victory or defeat, winning and losing, or the outcome of a battle.
There is a suggestion in Shinken Shobu that you train with serious and real intent, as we should train with the same fervor and dedication as if the battle was real. “Train as we fight.”
See Also: The More We Sweat in Training the Less We Bleed in Battle | Cry in the Dojo - Laugh on the Battlefield