1650s, "square," with -ic + obsolete quadrate "a square; a group of four things" (late 14c.), from Latin quadratum, noun use of neuter adjective quadratus "square, squared," past participle of quadrare "to square, set in order, complete" (see quadrant). Quadratic equations (1660s) so called because they involve the square of x.
Relating to a mathematical expression containing a term of the second degree, such as x2 + 2. ◇ A quadratic equation is an equation having the general form ax2 + bx + c = 0, where a, b, and c are constants. ◇ The quadratic formula is x = -b ± √(b2 - 4ac)/2a. It is used in algebra to calculate the roots of quadratic equations.