"of or occurring before the dawn of day," 1940, from pre- + dawn (n.).
Entries linking to pre-dawn
pre-
word-forming element meaning "before," from Old French pre- and Medieval Latin pre-, both from Latin prae (adverb and preposition) "before in time or place," from PIE *peri- (source also of Oscan prai, Umbrian pre, Sanskrit pare "thereupon," Greek parai "at," Gaulish are- "at, before," Lithuanian prie "at," Old Church Slavonic pri "at," Gothic faura, Old English fore "before"), extended form of root *per- (1) "forward," hence "beyond, in front of, before."
The Latin word was active in forming verbs. Also see prae-. Sometimes in Middle English muddled with words in pro- or per-.
dawn n.
1590s, "first appearance of daylight in the morning," from dawn (v.). Middle English words for "first appearance of light in the morning" were day-gleam (late 14c.), dayspring (c. 1300), and dawning. Dawn (n.) in the figurative sense of "first opening or expansion of anything" is from 1630s. As a fem. proper name, little used in U.S. before 1920 but a top 25 name for girls born 1966-1975.