heptad
(ˈhɛptæd)
[ad. Gr. ἑπτάς, ἑπταδ-, the number seven collectively.]
1. The sum or number of seven; a group of seven.
| 1660 Stanley Hist. Philos. ix. (1701) 383/2 The Heptad was so called, qu. σεπτὰς σεβασµοῦ ἄξιος worthy of veneration. 1797 Monthly Mag. III. 521 The heptad of wandering animals. 1850 J. Brown Disc. Our Lord (1852) I. iv. 351 This prayer contains a sacred heptad of petitions. |
b. spec. A group of seven days, a week; = hebdomad.
| 1876 tr. Keil & Delitzsch's Ezek. II. 336 A feast of heptads of days or weeks of days. 1881 Blackie Lay Serm. ii. 83 The months are divided into heptads. |
2. Chem. An atom or molecule whose equivalence is seven atoms of hydrogen, i.e. which can be combined with, substituted for, or replaced by seven atoms of hydrogen.
3. Mus. A scheme of seven tones in the duodenal system of analysis, containing all the notes from which consonant triads may be formed with the tonic.
| 1874 A. J. Ellis in Proc. R. Soc. XXIII. 11 The Harmonic Heptad or Unit of Chord-relationship..The heptad also contains all triads, consisting of three tones, two of which are consonant with C but dissonant with each other. |