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.
(chemistry) A variant of tri-, used for substitutions of three complex rather than simple units, as in,
trisbenzene-azophenol, C6H2(N:NC6H5)3OH
tristhio-dimethyl-benzaldehyde, {C6H3(CH3)2CHS}3