The Collaborative International Dictionary of English v.0.48:

Hemistich \Hem"i*stich\ (?; 277), n. [L. hemistichium, Gr.
   "hmisti`chion; "hmi- half + sti`chos row, line, verse: cf. F.
   h['e]mistiche.]
   Half a poetic verse or line, or a verse or line not
   completed.
   [1913 Webster]