S: (n) unit of measurement, unit (any division of quantity accepted as a standard of measurement or exchange) "the dollar is the United States unit of currency"; "a unit of wheat is a bushel"; "change per unit volume"
S: (n) photograph, photo, exposure, picture, pic (a representation of a person or scene in the form of a print or transparent slide or in digital format)
S: (n) exposure (the act of exposing film to light)