What is "tris-"

pre. 1 (context chemistry obsolete English) A variant of tri- used to indicate that the component that does ''not'' take the prefix occurs three times in the compound: '''''tris'''phosphuret of copper'' is PCu_'''3'''; '''tris'''benzeneazoresorcinol, C₆H(OH)₂(N₂Ph)_'''3'''. 2 (context chemistry English) A variant of tri-, used for substitutions of three complex rather than simple units, as in,