An Etymological Dictionary of Astronomy and Astrophysics

A flow in which the characterizing conditions, such as → streamlines or velocity at any given point, do not change with time.

Etymology (EN): → steady; → flow.

Etymology (PE): Tacân, → flow; pâyâ “steady, constant,” from
pâyidan “to stand firm, to be constant, steady,” from Mid.Pers. pattây-, pattutan “to last, endure, stay.”