in Algebra, an equation raised to the fourth power, or where the unknown quantity of one of the terms has four dimensions: Thus \(x^4 + ax^3 + bx^2 + cx + d = 0\) is a biquadratic equation. See ALGEBRA. Biquadratic Parabola, in Geometry, a curve line of the third order, having two infinite legs tending the same way. See Parabola.

Biquadratic Power of any number, is the fourth power or squared square of that number: Thus $16$ is the biquadratic power of $2$; for $2 \times 2 = 4$, and $4 \times 4 = 16$.

Biquadratic Root of any number, is the square root of the square root of that number: Thus the biquadratic root of $81$ is $3$; for the square root of $81$ is $9$, and the square root of $9$ is $3$.