E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Vindicate (3 syl.),
to justify, to avenge, has a remarkable etymon. Vindicius was a slave of the Vitelli, who informed the Senate of the conspiracy of the sons of Junius Brutus to restore Tarquin, for which service he was rewarded with liberty (Livy, ii. 5); hence the rod with which a slave was struck in manumission was called vindicta, a Vindicius rod (see MANUMIT); and to set free was in Latin vindicare in libertatem. One way of settling disputes was to give the litigants two rods, which they crossed as if in fight, and the person whom the prætor vindicated broke the rod of his opponent. These rods were called vindiciæ, and hence vindicate, meaning to justify. To avenge is simply to justify oneself by punishing the wrongdoer.