triumvir
noun
tri·um·vir trī-ˈəm-vər 
plural triumvirs also triumviri trī-ˈəm-və-ˌrī
-ˌrē
: one of a commission or ruling body of three
Word History
Etymology
Middle English, from Latin, back-formation from triumviri, plural, commission of three men, from trium virum of three men
First Known Use
15th century, in the meaning defined above