metrical foot, late 14c., from Latin dactylus, from Greek daktylos, a unit of measure (a finger-breadth), also "a fruit of the date tree, a date," literally "finger" (also "toe"), a word of unknown origin. The metrical use (a long syllable followed by two short ones) is by analogy with the three joints of a finger. In English versification it refers to an accented syllable followed by two unaccented. The "date" sense also sometimes was used in early Modern English.
"of the period before the date fixed for release," 1916, in reference to motion pictures, from pre- + release (n.). As a noun, "a film or record available on a limited basis before general release," by 1919. As a verb, "to release on a limited basis before the date fixed for release," by 1917 (implied in pre-released).
1580s, "person of the present time" (contrasted to ancient), from modern (adj.). From 1897 as "one who is up to date."