Talk:Celestia/@comment-98.245.184.201-20110814213345/@comment-6808267-20110817182516

They are called alicorns in Advanced Dungeons & Dragons(introduced in 2nd edition). That is where the the term "alicorn" as used in the MLP:FIM fandom comes from. So you can blame Wizards of the Coast for introducing the term to refer to a flying unicorn.