1590s, "blue pigment made from lapis lazuli," from Medieval Latin ultramarinus, literally "beyond the sea," from Latin ultra- "beyond" (from suffixed form of PIE root *al- "beyond") + marinus "of the sea," from mare "sea, the sea, seawater," from PIE root *mori- "body of water." Said to be so called because the mineral was imported from Asia.
It is the hypothetical source of/evidence for its existence is provided by: Latin mare; Old Church Slavonic morje, Russian more, Lithuanian marės, Old Irish muir, Welsh mor "sea;" Old English mere "sea, ocean; lake, pool," German Meer "sea."
"azure-stone, rich ultramarine silicate stone," early 15c., from Middle Latin lapis lazuli, literally "stone of azure," from Latin lapis "a stone" (see lapideous) + Medieval Latin lazuli, genitive of lazulum, from Arabic lazuward (see azure).