Is an oscillatory motion always periodic ?

[torquemaster]

Is an oscillatory motion always periodic ?


3 I think the answer is yes but the answer in my book was NO please explain

 

[Spinnor]

Periodic--occurring or appearing at regular intervals.

Say an oscillating system looses energy so that the max amplitude gets smaller with time and also suppose that the frequency of oscillation depends on the amplitude. This describes many real systems that oscillate. Is such motion periodic?