adj. 1. having the shape of a cube. 2. of, relating to, the third power. 3. (of an algebraic expression, equation, etc.) containing a variable raised to the third power, and none raised to a higher power; of the third degree. 4. (of an algebraic expression, equation, etc.) containing a term in which the variables have exponents the sum of which equals 3, and no term in which the exponents have a higher sum; of the third degree. 5. denoting a measure of three-dimensional space that is derived from a linear measure by raising it to the third power; thus a cubic meter is the volume enclosed by a cube each of the sides of which is one meter long. 6. (as substantive) a cubic equation, function, expression or term.