Premise: Brutus is a "cognomen" of the Roman "gens Junia", a prominent family of the Roman Republic. The plural of Brutus is "Bruti", and the vocative form is "Brute", as used in the quotation ""Et tu, Brute?"" ("you too, Brutus?"), from Shakespeare's play "Julius Caesar".
Hypothesis: Brutus is the singular of "Bruti"