According to Chambers an antiscian is "a dweller on the same meridian on the other side of the equator, whose shadow at noon falls in the opposite direction."
I can't for the life of me think why somebody should need a word for that. How often would one even write to one's anitiscian, let alone talk about him behind his back?
My OED has the word as well (with a plural of antiscii) but lists no uses, only an enigmatic date: 1706. Webster has antiscians, but the only usage he cites is Brande & Cox, which is another dictionary. It is also, I discover, an approved word in the Telegraphic Mining Dictionary, which is strange as miners are underground and don't cast shadows at noon, so they're the one lot of people who really couldn't have antiscii.
I fear my antiscian may have drowned. His nearest land is Bouvet Island and that's 238 miles away and Norwegian. I feel sure that my antiscian instinctively distrusts Norwegians.
A penguin hurries back to Bouvet Island with a message from my antiscian
P.S. It's pronounced antishian