Triad comes from Late Latin trias (stem triad-), from Ancient Greek trias ('a group of three'), from treis ('three'). The historical chain includes Ancient Greek trias, Ancient Greek treis, and Proto-Indo-European *treyes. The quoted older senses, "a group of three" and "three", supply the semantic anchors for triad. The formation is best read as borrowed: the word triad carries its older form-history into a compact English lexical shape. In present English it is used as a noun, "a group or set of three related things or people". English derivatives include triadic; related English forms include triangle, trinity, triple, and triplet. The result is a noun whose etymology preserves both the older form and the later English specialization.