decad
(ˈdɛkəd)
[ad. Gr. δεκάς, δεκαδ-, collective n. from δέκα ten.]
1. The number ten (the perfect number of the Pythagoreans).
| 1616 in Bullokar. 1655–60 Stanley Hist. Philos. (1701) 379/2 The Decad comprehends every Reason of Number, and every Proportion. 1865 Grote Plato I. i. 11 The Dekad, the full and perfect number. 1881 tr. Zeller's Presocratic Phil. I. 427 All numbers and all powers of numbers appeared to them [the Pythagoreans] to be comprehended in the decad. |
2. Music. A group of ten notes out of which may be formed the consonant triads, and all the discords possible without a modulation.
| 1875 A. J. Ellis tr. Helmholtz 663 Decad. |
3. An earlier spelling of decade, q.v.