The Collaborative International Dictionary of English v.0.48:

Inquiry \In*quir"y\, n.; pl. Inquiries. [See Inquire.]
   [Written also enquiry.]
   1. The act of inquiring; a seeking for information by asking
      questions; interrogation; a question or questioning.
      [1913 Webster]

            He could no path nor track of foot descry,
            Nor by inquiry learn, nor guess by aim. --Spenser.
      [1913 Webster]

            The men which were sent from Cornelius had made
            inquiry for Simon's house, and stood before the
            gate.                                 --Acts x. 17.
      [1913 Webster]

   2. Search for truth, information, or knowledge; examination
      into facts or principles; research; investigation; as,
      physical inquiries.
      [1913 Webster]

            All that is wanting to the perfection of this art
            will undoubtedly be found, if able men . . . will
            make inquiry into it.                 --Dryden.
      [1913 Webster]

   Court of inquiry. See under Court.

   Writ of inquiry, a writ issued in certain actions at law,
      where the defendant has suffered judgment to pass against
      him by default, in order to ascertain and assess the
      plaintiff's damages, where they can not readily be
      ascertained by mere calculation. --Burrill.

   Syn: Interrogation; interrogatory; question; query; scrutiny;
        investigation; research; examination.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Enquiry \En*quir"y\, n.
   See Inquiry.
   [1913 Webster]

WordNet (r) 3.0 (2006):

enquiry
    n 1: an instance of questioning; "there was a question about my
         training"; "we made inquiries of all those who were
         present" [syn: question, inquiry, enquiry, query,
         interrogation] [ant: answer]
    2: a search for knowledge; "their pottery deserves more research
       than it has received" [syn: inquiry, enquiry, research]
    3: a systematic investigation of a matter of public interest
       [syn: inquiry, enquiry]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "enquiry":
   ask, ask a question, ask about, ask questions, be curious,
   bring into question, burn with curiosity, demand, dig around for,
   dig up, gape, gawk, inquire, inquire of, interpellate, interrogate,
   make inquiry, nose around for, nose out, peer, propose a question,
   propound a question, put queries, query, question, quiz,
   require an answer, rubber, rubberneck, seek, stare, want to know