incessant

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Continuing without interruption. See Synonyms at continual.

Century Dictionary and Cyclopedia

1. Continued or repeated without interruption or intermission; unceasing; ceaseless: as, incessant rains; incessant clamor.
2. Synonyms Continuous, Incessant, Continual, Perpetual; unremitting, unremitted. Continuous means unbroken, and is passive; incessant means unceasing, and is active. The former is preferable to note duration, condition, or result; the latter, to describe the exertion by which the condition or result is produced. We speak of a continuous or an incessant fever, according as we think of the fever as a state or as an activity; and similarly of a continuous or incessant strain of music, and the continuous or incessant murmur of a brook; but only of a continuous railroad-track or telegraph-wire. Continual regularly implies the habitual or repeated renewals of an act, state, etc.: as, a continual succession of storms. In the Bible continual is sometimes used for continuous, but the distinction here indicated is now clearly established. Perpetual is continuous with the idea of lastingness: as, perpetual motion. It is often used in the sense of continual: as, I am sick of such perpetual bickerings. In either sense, unless the thing is really everlasting, it is used by hyperbole, as implying that one sees no end to the matter. See eternal.

Wiktionary

1. adj. Without pause or stop; not ending, especially to the point of annoyance.

GNU Webster's 1913

1. adj. Continuing or following without interruption; unceasing; unitermitted; uninterrupted; continual.

WordNet 3.0

1. adj. uninterrupted in time and indefinitely long continuing