The Collaborative International Dictionary of English v.0.48:

Interrogation \In*ter`ro*ga"tion\, n. [L. interrogatio: cf. F.
   interrogation.]
   [1913 Webster]
   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 +PJC]

   Note: In works printed in the Spanish language this mark is
         not only placed at the end of an interrogative
         sentence, but is also placed, inverted [as thus
         ([iques])], at the beginning.
         [1913 Webster]

WordNet (r) 3.0 (2006):

question mark
    n 1: a punctuation mark (?) placed at the end of a sentence to
         indicate a question [syn: question mark, interrogation
         point]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "question mark":
   Chinese puzzle, baffling problem, bone of contention,
   brain twister, catechism, cross-interrogatory, cross-question,
   crossword puzzle, crux, debating point, demand, enigma,
   enigmatic question, feeler, floorer, inquiry, interrogation,
   interrogative, interrogatory, issue, jigsaw puzzle, knot,
   knotty point, leader, leading question, mind-boggler, moot point,
   mystery, nut to crack, perplexed question, perplexity,
   point at issue, point in question, poser, problem, puzzle,
   puzzlement, puzzler, query, question, question at issue, quodlibet,
   sixty-four dollar question, sticker, stumper, topic,
   tough proposition, trial balloon, vexed question, why



The Free On-line Dictionary of Computing (30 December 2018):

question mark
?
ques

    "?", ASCII character 63.

   Common names: query; ITU-T: question mark; ques.  Rare:
   whatmark; INTERCAL: what; wildchar; huh; hook; buttonhook;
   hunchback.

   Question mark is used, along with colon for C's lazy
   triadic "if" operator (similar to the IIF function in
   Visual Basic).  The expression x?y:z evaluates x, then if x
   is true it returns y else it returns z.

   In Unix shell file name patterns, question mark matches
   any single character.

   (2003-06-17)