Each rotational degree of freedom contributes an energy term containing the square of a:

1. Translational terms are squares of velocity components. 2. Rotation follows the same pattern with its own variable. 3. Each rotational degree of freedom contributes a term containing the square of a rotational variable of motion. 4. So the answer is a rotational variable. _Source: syllabus Physics Part II, Ch 12 'Kinetic Theory'_