An Etymological Dictionary of Astronomy and Astrophysics

A suffix denoting the state of turning in a specified way.

Etymology (EN): From Gk. -tropia, from tropos “turn,” trope “a turning.”

Etymology (PE): Suffix form -gardi, from gardidan, gaštan “to turn, to change” (Mid.Pers. vartitan; Av. varət- “to turn, revolve;” Skt. vrt- “to turn, roll,” vartate “it turns round, rolls;” L. vertere “to turn;” O.H.G. werden “to become;” PIE base *wer- “to turn, bend”).