Properly a chariot chair, an ornamental camp-stool made of ivory placed by the Romans in a chariot for the chief magistrate when he went to attend the council. As dictators, consuls, praetors, censors, and the chief ediles occupied such a chair, they were termed curule magistrates or curules. Horace calls the chair curule ebur (1 Epist., vi. 53).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894