ADJECTIVE (2)

1. occurring without interruption; chiefly restricted to what recurs regularly or frequently in a prolonged and closely spaced series;
- Example: "the continual banging of the shutters"

2. `continual'; (meaning seemingly uninterrupted) is often used interchangeably with `continuous'; (meaning without interruption);

The Collaborative International Dictionary of English v.0.48:

Continual \Con*tin"u*al\, a. [OE. continuel, F. continuel. See
   Continue.]
   1. Proceeding without interruption or cesstaion; continuous;
      unceasing; lasting; abiding.
      [1913 Webster]

            He that is of a merry heart hath a continual feast.
                                                  --Prov. xv.
                                                  15.
      [1913 Webster]

   2. Occuring in steady and rapid succession; very frequent;
      often repeated.
      [1913 Webster]

            The eye is deligh by a continental succession of
            small landscapes.                     --W. Irwing.
      [1913 Webster]

   Continual proportionals (Math.), quantities in continued
      proportion. --Brande & C.

   Syn: Constant; prepetual; incessant; unceasing;
        uninterrupted; unintermitted; continuous. See
        Constant, and Continuous.
        [1913 Webster]

WordNet (r) 3.0 (2006):

continual
    adj 1: occurring without interruption; chiefly restricted to
           what recurs regularly or frequently in a prolonged and
           closely spaced series; "the continual banging of the
           shutters" [ant: sporadic]
    2: `continual' (meaning seemingly uninterrupted) is often used
       interchangeably with `continuous' (meaning without
       interruption)