1.  interrogation(n = noun.communication) interrogative, interrogative sentence, question - a sentence of inquiry that asks for a reply; "he asked a direct question"; "he had trouble phrasing his interrogations"
Derived form verb interrogate₂

2.  interrogation(n = noun.communication) - a transmission that will trigger an answering transmission from a transponder;
Derived form verb interrogate₁

3.  interrogation(n = noun.communication) examination, interrogatory - formal systematic questioning;
Derived form verb interrogate₂

4.  interrogation(n = noun.communication) enquiry, inquiry, query, question - an instance of questioning; "there was a question about my training"; "we made inquiries of all those who were present"
Derived form verb interrogate₂

1.  The act or process of interrogating or questioning; examination by questions; an instance of interrogating; inquiry. [1913 Webster]

2.  A question put; an inquiry. [1913 Webster]

3.  A point, mark, or sign, thus [?], indicating that the sentence with which it is connected is a question. It is used to express doubt, or to mark a query. Usually called a question mark; called also interrogation point. [1913 Webster]

interrogation, n.
1 the act or an instance of interrogating; the process of being interrogated.
2 a question or enquiry.

Idiom:
interrogation point (or mark etc.) = question mark.

Derivative:
interrogational adj.

Etymology:
ME f. F interrogation or L interrogatio (as INTERROGATE)

N  inquiry, request, search, research, quest, pursuit, examination, review, scrutiny, investigation, indagation, perquisition, perscrutation, pervestigation, inquest, inquisition, exploration, exploitation, ventilation, sifting, calculation, analysis, dissection, resolution, induction, Baconian method, strict inquiry, close inquiry, searching inquiry, exhaustive inquiry, narrow search, strict search, study, scire facias, ad referendum, trial, questioning, interrogation, interrogatory, interpellation, challenge, examination, cross-examination, catechism, feeler, Socratic method, zetetic philosophy, leading question, discussion, reconnoitering, reconnaissance, prying, espionage, espionnage, domiciliary visit, peep behind the curtain, lantern of Diogenes, question, query, problem, desideratum, point to be solved, porism, subject of inquiry, field of inquiry, subject of controversy, point in dispute, matter in dispute, moot point, issue, question at issue, bone of contention, plain question, fair question, open question, enigma, knotty point, quodlibet, threshold of an inquiry, inquirer, investigator, inquisitor, inspector, querist, examiner, catechist, scrutator scrutineer scrutinizer, analyst, quidnunc, inquiry, inquisitive, requisitive, requisitory, catechetical, inquisitorial, analytic, in search of, in quest of, on the lookout for, interrogative, zetetic, all searching, undetermined, untried, undecided, in question, in dispute, in issue, in course of inquiry, under discussion, under consideration, under investigation, sub judice, moot, proposed, doubtful, quaere?, what?, why?, wherefore?, whence?, whither?, where?, how comes it?, how happens it?, how is it?, what is the reason?, what's the matter?, nicht wahr?, what's in the wind?, what on earth?, when?, who?.