biquadratic vs equation

biquadratic and equation both are nouns.

Word	Noun	Adjective	Verb	Adverb
biquadratic	Yes	Yes	No	No
equation	Yes	No	No	No

As nouns, equation is a hypernym of biquadratic; that is, equation is a word with a broader meaning than biquadratic:

biquadratic (noun)	equation (noun)
a polynomial of the fourth degree	the act of regarding as equal
an equation of the fourth degree	a mathematical statement that two expressions are equal
an algebraic equation or function of the fourth degree	a state of being essentially equal or equivalent; equally balanced

biquadratic (adjective)	equation (adjective)
involving the fourth and no higher power of a quantity or degree