septenarius
noun
sep·te·nar·i·us ˌsep-tə-ˈner-ē-əs 
plural septenarii ˌsep-tə-ˈner-ē-ˌī
-ē-ˌē
: a verse consisting of seven feet especially in Latin prosody
Word History
Etymology
Latin, from septenarius of seven, from septeni seven each, from septem seven
First Known Use
1706, in the meaning defined above