Collective numerals; nymphs.
[Greek -as, -ad-.]
Examples of collective numerals include dyad, something that consists of two elements or parts, and triad, of three. A chiliad (Greek khilioi, a thousand) is either a group of a thousand or a period of a thousand years; a myriad is usually a countless or extremely great number (more strictly ten thousand, as it comes from the Greek murioi for that number). Decade, meaning ten or a period of ten years, retains its final e from French. In classical Greece an Olympiad was the period of four years between one Olympic Games and the next, though in modern English it often refers to a celebration of the games.
Names of nymphs in Greek classical mythology include dryad (Greek drus, tree), a nymph inhabiting a tree or a wood, and naiad (Greek naein, to flow), a water nymph said to inhabit a river, spring, or waterfall.