1540s, "tending to make peace, concillatory," from Middle French pacifique, from Latin pacificus "peaceful, peace-making," from pax (genitive pacis) "peace" (see peace) + combining form of facere "to make" (from PIE root *dhe- "to set, put"). Meaning "peaceful, characterized by peace or calm" is recorded from 1630s. Related: Pacifical (mid-15c., "of a peaceful nature"); pacifically.
Pacific, making or desiring to make peace; peaceable, desiring to be at peace, free from the disposition to quarrel; peaceful, in a state of peace. [Century Dictionary, 1895]
The Pacific Ocean (1660 in English) was famously so called in 1519 by Magellan when he sailed into it and found it calmer than the stormy Atlantic, or at least calmer than he expected it to be. According to an original account of the voyage by an Italian named Pigafetta, who was among the adventurers, Magellan gave the entrance to what Pigafetta calls "the South Sea" the Latin name Mare Pacificum. The U.S. Pacific Northwest is so called by 1889.