Definition of "biquadratic"

(mathematics) Of a polynomial expression, involving only the zeroth, second, and fourth powers of a variable, as x4 + 3x2 + 2. Sometimes extended to any expression involving the biquadrate or fourth power (but no higher powers), as x4 − 4x3 + 3x2 − x + 1.  examples

(mathematics) A biquadratic equation.  examples