tris-

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• prefix chemistry (obsolete) A variant of tri- used to indicate that the component that does not take the prefix occurs three times in the compound: trisphosphuret of copper is PCu3; trisbenzeneazoresorcinol, C6H(OH)2(N2Ph)3.
• prefix chemistry A variant of tri-, used for substitutions of three complex rather than simple units, as in,