One of the mysteries of the English language finally explained.
Definition of pietra commessa in English:
pietra commessa
noun
rareMosaic work of a type developed in Florence in the late 16th cent., consisting of thin pieces of coloured semi-precious stones cut to shape and inlaid in marble to produce decorative designs and pictures; Florentine mosaic; an example of this.
Origin
Mid 17th century; earliest use found in John Evelyn (1620–1706), diarist and writer. From Italian pietra commessa (apparently not recorded in Italian dictionaries) from pietra stone + commessa, feminine of commesso, past participle of commettere to fit together (from classical Latin committere).