a word used by some old writers for the number ten, and decades for an enumeration by No. 98.

The word is formed from the Latin decas, which is derived from a Greek word of the same import. The word has been more peculiarly appropriated to the number of books, q. d., decades, into which the Roman History of Titus Livius is divided. Hence also came decadal arithmetic, the Decameron of Boceacio, &c.