What decorative shellwork motif gave the Rococo style its name?

The decorative shellwork motif that gave the Rococo style its name was rocaille.

In French, rocaille referred to ornament made from rocks, pebbles, shells, and cement, especially in artificial grottoes, fountains, and garden structures. By the late 17th and early 18th centuries, the word also described elaborate interior decoration using shell forms, scrolling foliage, and asymmetrical curves.

Rocaille designs appeared on furniture, wall panels, mirrors, doorways, and architectural details. The term rococo developed later as a satirical or critical variation of rocaille, initially implying excessive or old-fashioned ornament rather than serving as a neutral style label.

A common mix-up is to treat chinoiserie or arabesque as the source of the name. Both were important decorative influences in 18th-century interiors, but neither supplied the word rococo. Rocaille is the specific shell-centered motif and the linguistic root associated with the style.