In planetary nomenclature, a tholus (pl. tholi) is a small domical mountain or hill. The word is from the Greek θόλος, tholos (pl. tholoi), which means a circular building with a conical or vaulted roof. The Romans transliterated the word into the Latin tholus, which means cupola or dome.[1] In 1973, the International Astronomical Union (IAU) adopted tholus as one of a number of official descriptor terms for topographic features on Mars and other planets and satellites.[2] One justification for using neutral Latin or Greek descriptors was that it allowed features to be named and described before their geology or geomorphology could be determined.[3] For example, many tholi appear to be volcanic in origin, but the term does not imply a specific geologic origin.[4] Currently (March 2015), the IAU recognizes 56 descriptor terms. (See Planetary nomenclature.) Tholi are present on Venus, Mars, asteroid 4 Vesta, dwarf planet Ceres, and on Jupiter's moon Io.