A license with no expiration date.

(finance) A bond with no maturity date, paying coupons forever.

plural of perpetual license

(physics, pseudoscience) A hypothetical device that exhibits perpetual motion, especially one that does useful work with no input of energy.

plural of perpetual motion machine

plural of self-perpetuation

Causing itself to continue to exist.

An act or state of something causing itself to continue to exist.

Contentment is more a matter of attitude than circumstances.

(law, singular only) The rule that prevents a testator or other transferor of property from controlling further transfer of his property more than twenty-one years after the death of anyone alive at the time of the original transfer who may have some interest in the transfer.