Europe and Asia are not two separate islands. They sit on one unbroken stretch of land, and that whole stretch has a name: Eurasia. Eurasian points at that whole stretch at once. So a Eurasian trade route is one that runs the length of it, and the Eurasian plate is the sheet of rock that lies under it. Nature writing uses the word the same way. The Eurasian otter is called that because it turns up from Britain across to Japan, not because it belongs to one country. The word keeps its capital E, because it is built out of the names of the two continents.

This is the same idea as the adjective, packed into a noun. Instead of saying a Eurasian writer, older books simply say a Eurasian. The plural is Eurasians. The fuller source entry gives a looser version, a person of mixed European and Asian ancestry, which does not insist on the parents themselves. The old-fashioned label is the part a learner needs most: recognise the word when you meet it in an older novel or an old record, and say the two backgrounds plainly when you are writing about a person now.

Here the word has moved off the map and onto a person. The two continents that meet in the land are now the two sides of one family. The learner dictionary keeps it narrow: one European parent and one Asian parent. The fuller source entry is looser and says only mixed European and Asian ancestry, which covers a grandparent as well. Both sources are describing the same idea from different distances. The label matters as much as the meaning: old-fashioned tells you the word carries the flavour of older books, older papers and older magazines, so naming the two backgrounds directly is usually the clearer choice when you are describing someone today.