I tend to think in terms of Atlantic and Pacific when I think of oceans, but these names had not solidified in the 18th century.
This article,
Naming the Pacific, gives a thorough history of the names that were used for the oceans and the surrounding landmasses (and theoretical landmasses).
The Atlantic was primarily thought of as the North Sea, while the Pacific was termed the South Sea (since they traveled south to reach it) - a name which persisted well into the 19th century.