1. Recurring regularly or frequently: the continual need to pay the mortgage.
2. Not interrupted; steady: continual noise; a continual diet of vegetables.

Synonyms: These adjectives mean occurring repeatedly over a long period of time. Continual is chiefly restricted to what is intermittent or repeated at intervals: The continual banging of the shutter in the wind gave me a headache.
Continuous implies lack of interruption: The horizon is a continuous line.
Constant stresses steadiness or persistence and unvarying nature: The constant ticking of the clock lulled him to sleep.
Ceaseless and incessant pertain to uninterrupted activity: The ceaseless thunder of the surf eroded the beach. The toddler asked incessant questions.
Perpetual emphasizes both steadiness and duration: The ambassador had a perpetual stream of visitors.
Eternal refers to what is everlasting, especially to what is seemingly without temporal beginning or end: "That freedom can be retained only by the eternal vigilance which has always been its price" (Elmer Davis).
Perennial describes existence that goes on year after year, often with the suggestion of self-renewal: The candidates discussed the perennial problem of urban poverty.
Interminable refers to what is or seems to be endless and is often applied to something prolonged and wearisome: After an interminable delay, our flight was canceled outright.