Nouns

(n)biquadrate, biquadratic, quartic, fourth poweran algebraic equation or function of the fourth degree
(n)biquadratic equation, biquadratican equation of the fourth degree
(n)biquadratic, biquadratic polynomial, quartic polynomiala polynomial of the fourth degree

Adjectives

(a)biquadraticinvolving the fourth and no higher power of a quantity or degree