The Collaborative International Dictionary of English v.0.48:

Interior \In*te"ri*or\, a. [L., compar. fr. inter between: cf.
   F. int['e]rieur. See Inter-, and cf. Intimate.]
   [1913 Webster]
   1. Being within any limits, inclosure, or substance; inside;
      internal; inner; -- opposed to exterior, or
      superficial; as, the interior apartments of a house; the
      interior surface of a hollow ball.
      [1913 Webster]

   2. Remote from the limits, frontier, or shore; inland; as,
      the interior parts of a region or country.
      [1913 Webster]

   Interior angle (Geom.), an angle formed between two sides,
      within any rectilinear figure, as a polygon, or between
      two parallel lines by these lines and another intersecting
      them; -- called also internal angle.

   Interior planets (Astron.), those planets within the orbit
      of the earth.

   Interior screw, a screw cut on an interior surface, as in a
      nut; a female screw.

   Syn: Internal; inside; inner; inland; inward.
        [1913 Webster]

WordNet (r) 3.0 (2006):

interior angle
    n 1: the angle inside two adjacent sides of a polygon [syn:
         interior angle, internal angle]