The Collaborative International Dictionary of English v.0.48:

Trigeminous \Tri*gem"i*nous\, a. [L. trigeminus born three
   together; tri- (see Tri-) + geminus twin. Cf.
   Tergeminous.]
   Born three together; being one of three born at the same
   birth; also, threefold. --E. Phillip?.
   [1913 Webster]