1580s, in Greek mythology a member of the older family of Gods, later regarded as a Titan, son of Iapetus and Clymene; in either case supposed to uphold the pillars of heaven (or earth), which according to one version was his punishment for being the war leader of the Titans in the struggle with the Olympian gods. "Originally the name of an Arcadian mountain god; the name was transferred to the mountain chain in Western Africa" [Beekes].
The Greek name traditionally is interpreted as "The Bearer (of the Heavens)," from a-, copulative prefix (see a- (3)), + stem of tlenai "to bear," from PIE root *tele- "to lift, support, weigh." But Beekes compares Berber adrar "mountain" and finds it plausible that the Greek name is a "folk-etymological reshaping" of this. Mount Atlas, in Mauritania, was important in Greek cosmology as a support of the heavens.
"collection of maps in a volume," 1636, first in the title of the English translation of "Atlas, sive cosmographicae meditationes de fabrica mundi" (1585) by Flemish geographer Gerhardus Mercator, who might have been the first to use this word in this way. A picture of the Titan Atlas holding up the world appeared on the frontispiece of this and other early map collections.