“Synthesia” is probably an amalgam of “synthesis,synthetic” and “synesthesia”. You would really have to ask the author to find out. Edit: It's worth pointing o

“Synthesia” is probably an amalgam of “synthesis,synthetic” and “synesthesia”. You would really have to ask the author to find out. Edit: It's worth pointing out that while the words look quite alike, they don't mean the same thing, synthesis: to put together aesthesia: ability to feel or perceive sensations