Although usage guides generally advise that continual may be used only to mean “intermittent” and continuous only to mean “uninterrupted,” the words are used interchangeably in all kinds of speech and writing with no distinction in meaning: The president's life is under continual (or continuous) scrutiny. Continuous (or continual) bursts of laughter punctuated her testimony. The adverbs continually and continuously are also used interchangeably. To make a clear distinction between what occurs at short intervals and what proceeds without interruption, writers sometimes use the contrasting terms intermittent (intermittent losses of power during the storm) and uninterrupted (uninterrupted reception during the storm) or similar expressions. Continuous is not interchangeable with continual in the sense of spatial relationship: a continuous (not continual) series of passages.
mid-14c., continuell, from O.Fr. continuel (12c.), from L. continuus (see continue). That which is continual is that which is either always going on or recurs at short intervals and never comes to an end; that which is continuous is that in which there is no break between the beginning and the end. Related: Continually (c.1300, contynuelliche).