An astrologer who is a devout follower and proponent of the work of the 17th century astrologer William Lilly. Often used in a derogatory sense to indicate that this person is a fundamentalist of sorts, or is a bit narrow in the scope of their astrological interests.
John: Hey, did you hear that Tom will be speaking at that astrological conference next year? What do you think of him?
Rob: Meh. Tom's a total Lillyite. He acts like Lilly's book is the Bible, and rejects anything else that isn't in his work. I try to be more open-minded. I'll pass.