An Etymological Dictionary of Astronomy and Astrophysics

Of or relating to or resembling a → square.
Of, relating to, or containing terms with powers no higher than the power of two.

Etymology (EN): Quadratic, adj. of quadrate, from L. quadratus p.p. of quadrare “to make square.”

Etymology (PE): Câruši pertaining to
câruš “square,” from Av. caθruša- “four sides (of a four-sided figure),”
from caθru- “four,” Mod.Pers. cahâr, câr “four,” cognate with L. quattuor, → four.