pen·tar·chy 
(pĕntär′kē)
(pĕntär′kē)n. pl. pen·tar·chies
1. Government by five rulers.
2. A body of five joint rulers.
3. An association or federation of five governments, each ruled by a different leader.
[Greek pentarkhiā : penta-, penta- + -arkhiā, -archy.]
pen·tarchi·cal (pĕn-tärkĭ-kəl) adj.