The synonyms perennial and perpetual are sometimes interchangeable, but perennial implies enduring existence often through constant renewal.

// a perennial source of controversy

Some common synonyms of perpetual are constant, continual, continuous, incessant, and perennial. While all these words mean "characterized by continued occurrence or recurrence," perpetual suggests unfailing repetition or lasting duration.

// a land of perpetual snowfall

In some situations, the words incessant and perpetual are roughly equivalent. However, incessant implies ceaseless or uninterrupted activity.

// annoyed by the incessant quarreling