The Collaborative International Dictionary of English v.0.48:
Modiolus \Mo*di"o*lus\, n.; pl. Modioli. [L., a small measure.] (Anat.) The central column in the osseous cochlea of the ear. [1913 Webster]WordNet (r) 3.0 (2006):
modiolus n 1: the central conical bony pillar of the cochlea