Fornix (plural, fornices), comes directly from the Latin word for a vault, i.e., a small room with an arched ceiling. Often the term was by the Romans in specific reference to rooms occupied by slaves or the poor. Street prostitutes were known to provide their services in fornices; hence the word "fornication".

The use of fornix in anatomy includes:

• The left and right fornices of the brain's limbic system, formed by white matter tracts that arch over the diencephalon,
  
• The vaginal fornix, the vaulted space in the vagina that surrounds the cervix of the uterus
• The gastric fornix, a term used in radiology for the internal arch of the fundus.
  

A series of fornices in Roman ruins, Gaeta, Italy, with the front walls and doors long gone. Modifed from A Dictionary of Roman Antiquities, by Antony Rich, Appelton, 1874.