The Collaborative International Dictionary of English v.0.48:

Interrogatory \In`ter*rog"a*to*ry\, n.; pl. Interrogatories.
   [Cf. F. interrogatoire.]
   A formal question or inquiry; esp. (Law), a question or
   series of questions asked in writing, usually as part of a
   lawsuit. --Macaulay.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Interrogatory \In`ter*rog"a*to*ry\, a. [L. interrogatorius.]
   Containing, expressing, or implying a question; as, an
   interrogatory sentence.
   [1913 Webster]

WordNet (r) 3.0 (2006):

interrogatory
    adj 1: relating to the use of or having the nature of an
           interrogation [syn: interrogative, interrogatory]
           [ant: asserting(a), declarative, declaratory]
    n 1: formal systematic questioning [syn: interrogation,
         examination, interrogatory]