\Tri-\ [Gr. tri- or L. tri-, sometimes through French; akin
to L. tres three, and E. three. See {Three}.]
1. A prefix meaning three, thrice, threefold; as in
   tricolored, tridentate.

2. (Chem.) A prefix (also used adjectively) denoting three
   proportional or combining part, or the third degree of
   that to the name of which it is prefixed; as in
   trisulphide, trioxide, trichloride.