Demi

Demi is a prefix meaning "half", loaned from French; for example, demi frere which means "half brother" or demi soeur which means "half sister". Demi-glace is made by simmering and reducing by half a mixture of half brown stock and half espagnole sauce.

Demi also has Latin roots as a feminine given name, originally a nickname form of Demetria, the feminine form of the masculine name Demetrius, which is itself the Latin and English spelling of Greek name Demetrios.
Demi is uncommon as a surname. People with the given name Demi include:
Demi Lovato (b. 1992), American actress and singer-songwriter
Demi (author) (b. 1942), American children's book author
Demi Delia (b. 1967), adult actress
Demi Moore (b. 1962), American actress
Demi Orimoloye (b. 1997), Canadian baseball player
Demy (singer) (b. 1991), Greek singer