Meaning of dedendum

de•den•dum

Pronunciation: (di-den'dum), [key]
— pl. -da
  1. (on a gear or rack) the radial distance between the pitch circle or line and the root circle or line. Cf. addendum (def. 3a).
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.