1) Group of ten tones 2) Mesopotamian deity 3) Number ten 1) Ten 
[Sumerian texts] The Decad is a name given to a standard sequence of ten scribal training compositions in ancient Sumer. == Sources and Evidence== The grouping of compositions known as the Decad is attested in several literary catalogues of tablets dating to Mesopotamia`s Old Babylonian period. Sumerian literary catalogues were lists of lit...
• (n.) A decade.
Dec'ad noun A decade. « Averill was a decad and a half his elder.» Tennyson.