Where do the terms highroad, highway, high seas, high tea come from?

It was not that the road, sea, way, or the like was elevated above others of its kind that it was labeled high, tracing back to Old English times, but that it possessed some quality that made it outstanding, especially notable.

The highroad and highway were main or principal roads; the high seas were oceans; high Mass was celebrated in full ceremonial.

And in a later day, high tea was an evening meal at which meat was served.