The Collaborative International Dictionary of English v.0.48:

Hendecasyllable \Hen*dec"a*syl`la*ble\, n. [L. hendecasyllabus,
   Gr. ? eleven-syllabled; ? eleven + ? syllable: cf. F.
   hend['e]casyllabe.]
   A metrical line of eleven syllables. --J. Warton.
   [1913 Webster]