According to the Oxford English Dictionary Atlantic first appears in Late Middle English. It was adopted from the Latin Atlanticus, which in turn came from the Greek Atlantikos, which in turn came from Atlant- and the god Atlas.

But how did the god Atlas get associated with the what we call the Atlantic Ocean? I’m glad you asked. Atlas was the Titan who warred against the gods led by Zeus. When they were defeated, Atlas was condemned to carry the heavens upon his shoulders – the image of him holding a globe on his aching shoulders is very iconic.

Atlas was associated with the sea from an early time. Some of the Homeric poems describes him as knowing the depths of the sea. The family tree of Greek gods is rather convoluted, to say the least, but in some versions Atlas is the god Oceanus’ nephew. Atlas coupled with the sea nymph Pleione, who gives birth to the Pleiades. The constellation Pleiades were important to the ancient mariners – Hesiod warns that when they dipped below the horizon in the winter it was a sign that sailing season was over.

So Atlas was vaguely associated with the ocean, but later authors begin to nail him down a bit more. Sometimes he is described as a mountain holding up the heavens. Where exactly this mountain was depends upon which writer you read, but eventually it become popular to say it was in northwest Africa. In fact, there is a mountain range there still called the Atlas Mountains. This geography was still a bit hazy, but Atlas is associated with the ocean and the far west (to the ancient Greeks). So there were writers as early as Herodotus who named the vast ocean past the pillars of Hercules after Atlas. By the early Roman Empire this seemed to be a common belief, and Valerius Flaccus placed Atlas off the African coast in the ocean which now bears his name.