How to obtain:
A broom made out of copper. (Scrub stubborn stains as you sweep!)
A "besom" is a broom or a bundle of twigs used as a broom. Cu is the Elemental Symbol for Copper (cuprum), which is 1/3 of the makings for the Besom Cu29. 29 also happens to be the Atomic Number for Copper.
From: Weapons (Chrono Cross)