Flywheel

[Tina]

A description applied to a girl with [large breasts], a large butt, but who is otherwise thin and [scrawny]. The term comes from the fact that she is distributed weight-wise similar to a [flywheel], implying that if she started to fall she would roll.

[Oralee]

a heavy wheel in a machine that helps the machine to work at a regular speed

[Ernesto]

A heavy revolving wheel in a machine that is used to increase the machines momentum and thereby provide greater stability or a reserve of available power during interruptions in the delivery of power to the machine.