1) Biquadratic 2) Fourth power 3) Number 4) Quartic 5) The fourth power 1) Quartic 
• (n.) The fourth power, or the square of the square. Thus 4x4=16, the square of 4, and 16x16=256, the biquadrate of 4.
Bi·quad'rate noun [ Prefix bi- + quadrate .] (Math.) The fourth power, or the square of the square. Thus 4x4=16, the square of 4, and 16x16=256, the biquadrate of 4. 
[n] - an algebraic equation of the fourth degree
biquadratic noun an algebraic equation of the fourth degree
the fourth power.