disdiaclast

from The Collaborative International Dictionary of English v.0.48

Disdiaclast \Dis*di"a*clast\, n. [Gr. di`s- twice + diakla^n to
   break in twain; dia` through + kla^n to break.] (Physiol.)
   One of the dark particles forming the doubly refracting disks
   of muscle fibers.
   [1913 Webster]