The Collaborative International Dictionary of English v.0.48:

Caption \Cap"tion\, n. [L. captio, fr. caper to take. In senses
   3 and 4, perhaps confounded in meaning with L. caput a head.
   See Capacious.]
   1. A caviling; a sophism. [Obs.]
      [1913 Webster]

            This doctrine is for caption and contradiction.
                                                  --Bacon.
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   2. The act of taking or arresting a person by judicial
      process. [R.] --Bouvier.
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   3. (Law) That part of a legal instrument, as a commission,
      indictment, etc., which shows where, when, and by what
      authority, it was taken, found, or executed. --Bouvier.
      --Wharton.
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   4. The heading of a chapter, section, or page. [U. S.]
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WordNet (r) 3.0 (2006):

caption
    n 1: taking exception; especially a quibble based on a captious
         argument; "a mere caption unworthy of a reply"
    2: translation of foreign dialogue of a movie or TV program;
       usually displayed at the bottom of the screen [syn:
       subtitle, caption]
    3: brief description accompanying an illustration [syn:
       caption, legend]
    v 1: provide with a caption, as of a photograph or a drawing