gadroon (gah-DRUNE) n. a form of decorative fluting; a type of notched architectural molding; oval-shaped or egg-shaped beadings or reedings used to adorn such items as molding or silverware; a convex band of short lengths of reeding that curve in a spiral pattern either to the left or to the right.
The word gadroon is derived from the French word godron ("rounded plait"), which itself comes from the Latin word guttus ("flask"). I think it is easier to present a visual depiction of a gadroon pattern than it is to verbally describe the concept of gadroon, perhaps in keeping with Elvis Costello's observation that "writing about music is like dancing about architecture." Anyways, here is a picture of gadroon molding to help you get the idea:
I came across the term gadroon while perusing an 1814 edition of Niles' Weekly Register on an unrelated search (no, the patent medicines of the day did not include precursors to phentermine).
Gadroon forms were much more common in Elizabethan and Italian Renaissance architecture, though the style has a certain timelessness to it. Some scholars suggest that gadrooning has its origins in medieval Islamic architecture, and that European architects absorbed the style after contacts with Islamic cultures. The following link has an image of the 12th century shrine of Zayn al-Din Yusuf, which features a gadrooned dome over the sheik's tomb.