adjective. Not tending toward a state of rest; not damped. Used of oscillations.

adjective. Not stifled or discouraged; unchecked.

adjective. of which the amplitude does not change over time

"This discovery was of importance, as it was found that the waves so generated were undamped, that is, capable of proceeding to their destination without loss of amplitude."

costless  dead-on  deader  escape-proof  motiveless