τετρακτύς,ύος,ἡ, (τετράς) Pythagorean name for
A. the sum of the first four numbers, i.e. 10 (= 1 + 2 + 3 + 4 ), ναὶ μὰ τὸν ἁμετέρᾳ ψυχᾷ παραδόντα τετρακτύν, παγὰν ἀενάου φύσεως
Carm.Aur. 48
, cf. S.E. M. 7.94 , TheoSm. p.94 H., Hierocl. in CA 20p.465M.
II. the four terms( 6 : 8 : 9 : 10 )of the proportion corresponding to the chief musical intervals, Nicom. Exc. 7 , 10 ; alsotheir sum+ 1 (= 36 ), ibid.;the sum of the first
8
numbers, Plu. 2.381f .