quin·quen·ni·um 
(kwĭn-kwĕnē-əm, kwĭng-)
(kwĭn-kwĕnē-əm, kwĭng-)n. pl. quin·quen·ni·ums or quin·quen·ni·a (-kwĕnē-ə)
A period of five years.
[Latin quīnquennium : quīnque, quinque- + annus, year; see at- in the Appendix of Indo-European roots.]