Ethroplanic

(ETH-row-PLAN-ick) An adjective, describing the look on a person’s face when their mind has clearly wandered somewhere distant. Derived from the Greek word αἰθροπλάνης, meaning “wandering through ether.”

More particularly, ethroplanic expressions occur in the middle of interactions; if I assumed a far-off look while by myself, it would not qualify as ethroplanic. But if I had been talking to you, and a silence occurred, and you looked over at me and my facial expression told you that I had gone somewhere else mentally, then you could say “you look rather ethroplanic.” Or you could say I had “gone ethroplanic” on you.