The Collaborative International Dictionary of English v.0.48:

Topic \Top"ic\, n. [F. topiques, pl., L. topica the title of a
   work of Aristotle, Gr. topika`, fr. topiko`s of or for place,
   concerning to`poi, or commonplaces, fr. to`pos a place.]
   (a) One of the various general forms of argument employed in
       probable as distinguished from demonstrative reasoning,
       -- denominated by Aristotle to`poi (literally, places),
       as being the places or sources from which arguments may
       be derived, or to which they may be referred; also, a
       prepared form of argument, applicable to a great variety
       of cases, with a supply of which the ancient rhetoricians
       and orators provided themselves; a commonplace of
       argument or oratory.
   (b) pl. A treatise on forms of argument; a system or scheme
       of forms or commonplaces of argument or oratory; as, the
       Topics of Aristotle.
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             These topics, or loci, were no other than general
             ideas applicable to a great many different
             subjects, which the orator was directed to consult.
                                                  --Blair.
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             In this question by [reason] I do not mean a
             distinct topic, but a transcendent that runs
             through all topics.                  --Jer. Taylor.
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   2. An argument or reason. [Obs.]
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            Contumacious persons, who are not to be fixed by any
            principles, whom no topics can work upon. --Bp.
                                                  Wilkins.
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   3. The subject of any distinct portion of a discourse, or
      argument, or literary composition; also, the general or
      main subject of the whole; a matter treated of; a subject,
      as of conversation or of thought; a matter; a point; a
      head.
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   4. (Med.) An external local application or remedy, as a
      plaster, a blister, etc. [Obsoles.] --Wiseman.
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The Collaborative International Dictionary of English v.0.48:

Topic \Top"ic\, a.
   Topical. --Drayton. Holland.
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WordNet (r) 3.0 (2006):

topic
    n 1: the subject matter of a conversation or discussion; "he
         didn't want to discuss that subject"; "it was a very
         sensitive topic"; "his letters were always on the theme of
         love" [syn: subject, topic, theme]
    2: some situation or event that is thought about; "he kept
       drifting off the topic"; "he had been thinking about the
       subject for several years"; "it is a matter for the police"
       [syn: topic, subject, issue, matter]