An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A suffix denoting "turned toward" that specified by the initial element; → barotropic, → isotropic, → polytropic.

From Gk. -tropos "a turn, way, manner," from tropein "to turn," from PIE base *trep- "to turn" (cf. L. trepit "he turns").

Gard "turning, changing," from gardidan "to turn, to change," Mid.Pers. vartitan, Av. varət- "to turn, revolve," Skt. vartati, L. vertere, O.H.G. werden "to become;" PIE *werto, *wer-.