Roget's Thesaurus of English Words and Phrases by Peter Mark Roget

tripartition†, trichotomy; third, third part. V. trisect, divide into three parts. Adj. trifid; trisected &c v.; tripartite, trichotomous†, trisulcate†. Triadelphous†, triangular, tricuspid, tricapsular†, tridental†, tridentate, tridentiferous†, trifoliate, trifurcate, trigonal†, trigrammic†, trigrammatic†, tripetalous†, tripodal, tripodic†, triquetral†, triquetrous†.