What is the meaning of Decad?

Archaic form of decade (period of ten years).

Archaic form of decade (group of ten).

A group of ten notes from which the consonant triads may be constructed

inflection of decădea:

  1. first-person singular present indicative/subjunctive
  2. third-person plural present indicative

first-person singular present indicative/subjunctive

third-person plural present indicative

Source: wiktionary.org