/euh den"deuhm/ , n. , pl. addenda /-deuh/ for 1, 2; addendums for 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 called addendum circle . an imaginary circle touching the tips of the teeth on a gear.
[ 1785-95; neut. sing. of L addendus to be added, gerundive of addere to ADD ]