Short form of Demetria. Demi is a diminutive of Demetria. Demetria originates in Greek language and means "mother of land". It is a feminine form of Demetrius, ultimately derived from Demeter. In Greek mythology, Demeter was a goddess of earth, agriculture, harvest and forests. Ceres would be her equivalent in Roman mythology. The name Demi was popularized by its famous bearer, the American actress Demi Moore, who was in fact born Demetria.