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The Teral'n in Nero's hand
The Teral'n was a Romulan staff weapon that had two retracting blades.
In 2387 Nero kept a Teral'n onboard his ship, the Narada. Nero had the weapon in hand when the Narada accidentally traveled back in time to 2233, creating an alternate reality. He used it to kill Captain Richard Robau of the USS Kelvin in 2233. (Star Trek)
Appendices
Apocrypha
Nero's acquiring of the Teral'n is explained in Star Trek: Countdown. In the book, the Teral'n (referred to as the "Debrune Teral'n") was an ancient weapon which served as the greatest symbol of the Romulan Star Empire. In the book, the praetor was in possession of the Teral'n when he and the ruling council of the Romulan Senate were beamed aboard the Narada following the destruction of Romulus. Angered that the Senate refused to believe Romulus was in danger, Nero took the Teral'n for himself and used it to kill the entire Senate.