The Collaborative International Dictionary of English v.0.48:

Interpellate \In`ter*pel"late\, v. t. [See Interpel.]
   To question imperatively, as a minister, or other executive
   officer, in explanation of his conduct; -- generally on the
   part of a legislative body.
   [1913 Webster]

WordNet (r) 3.0 (2006):

interpellate
    v 1: question formally about policy or government business