Pronunciation: (u-den'dum),[key] —n., —pl.-daPronunciation: (-du)[key]for 1, 2;-dumsfor 3. 1. a thing to be added; an addition.
2. an appendix to a book.
3. Mach. a. the radial distance between the tip of a gear tooth and the pitch circle of a gear or the pitch line of a rack. Cf. dedendum. b. Also calledadden'dum cir'cle. an imaginary circle touching the tips of the teeth on a gear.