camera lucida – An optical device consisting of an attachment that enables an observer to view simultaneously the image and a drawing surface for sketching it. More…
horoscope – Comes from Greek hora, “hour, time,” and skopos, “observer.” More…
obverse – Its first meaning was “turned towards or facing the observer.” More…
zenith, nadir – Zenith derived from Arabic samt ar-ras, “the way or road above one’s head”; zenith technically is the point directly above the observer and nadir is the point directly below. More…