hemistich
noun
hemi·stich ˈhe-mi-ˌstik 
: half a poetic line of verse usually divided by a caesura
Word History
Etymology
Latin hemistichium, from Greek hēmistichion, from hēmi- + stichos line, verse; akin to Greek steichein to go — more at stair
First Known Use
1575, in the meaning defined above