**Bi`quad*rat"ic** (?), a. [Pref. *bi-* + *quadratic*: cf. F. *biquadratique*.] Math.

Of or pertaining to the biquadrate, or fourth power.

Biquadratic equation Alg., an equation of the fourth degree, or an equation in some term of which the unknown quantity is raised to the fourth power. -- Biquadratic root of a number, the square root of the square root of that number. Thus the square root of 81 is 9, and the square root of 9 is 3, which is the *biquadratic** root of 81. Hutton.
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*© Webster 1913.
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***Bi`quad*rat"ic**, n. Math. (a)

A biquadrate.

(b)

A biquadratic equation.

*© Webster 1913.*