The Collaborative International Dictionary of English v.0.48:

Interior \In*te"ri*or\, n.
   1. That which is within; the internal or inner part of a
      thing; the inside.
      [1913 Webster]

   2. The inland part of a country, state, or kingdom.
      [1913 Webster]

   Department of the Interior, that department of the
      government of the United States which has charge of
      pensions, patents, public lands and surveys, the Indians,
      education, etc.; that department of the government of a
      country which is specially charged with the internal
      affairs of that country; the home department.

   Secretary of the Interior, the cabinet officer who, in the
      United States, is at the head of the Department of the
      Interior.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Secretary of the Interior
    n 1: the position of the head of the Department of the Interior;
         "the position of Interior Secretary was created in 1849"
         [syn: Secretary of the Interior, Interior Secretary]
    2: the person who holds the secretaryship of the Interior
       Department; "President Taylor appointed Thomas Ewing as the
       first Secretary of the Interior" [syn: Secretary of the
       Interior, Interior Secretary]