Dekad

Part of speech: noun

Definitions

1. A set or collection made up of exactly ten things ; a span of ten days or ten years marked off as a unit of time
2. A grouping of ten items taken together ; a stretch of ten consecutive days or years counted as one period
3. Ten things considered as a single unit ; a block of ten days or ten years treated as a distinct interval

Etymology: "Dekad" is a doublet of "decad" and "decade," all three descending from the same Ancient Greek noun, "dekas," meaning "group of ten." The Greek word was built from "deka," "ten," which also sits behind the decimal system, so the core idea has always been a set of ten things before anything else. The Greek noun passed into English along more than one route, which is why the spellings diverged. "Dekad" is the most direct borrowing of the Greek form, while "decad" and "decade" reflect later adjustments in spelling and sense. Over time the English descendants picked up different jobs: "decade" settled into the meaning of a span of ten years, whereas "dekad" and its near relative "decad" stayed closer to the plain counting sense of a group of ten.

Synonyms: decade, ten-day period