[syn: accessory, appurtenance, supplement, add-on]
WordNet (r) 3.0 (2006):
add-on
    n 1: a component that is added to something to improve it; "the
         addition of a bathroom was a major improvement"; "the
         addition of cinnamon improved the flavor" [syn: addition,
         add-on, improver]
    2: a supplementary component that improves capability [syn:
       accessory, appurtenance, supplement, add-on]
Easton's 1897 Bible Dictionary:
Addon
   low, one of the persons named in Neh. 7:61 who could not "shew
   their father's house" on the return from captivity. This, with
   similar instances (ver. 63), indicates the importance the Jews
   attached to their genealogies.
Hitchcock's Bible Names Dictionary (late 1800's):
Addon, basis; foundation; the Lord