Diamond Flower Brooch Mounted En Tremblant c. 1870. Image courtesy of Christie's

"En tremblant" is a French term - meaning "to tremble". It was first used to describe 18th and 19th century jewelry where parts of the diamond set pieces were attached to a trembler to create movement in the jewel when worn. Brooches in particular were fitted this way which was particularly effective in reflecting the fire of candlelight.