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.
      [1913 Webster]

   2. The act of taking or arresting a person by judicial
      process. [R.] --Bouvier.
      [1913 Webster]

   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.
      [1913 Webster]

   4. The heading of a chapter, section, or page. [U. S.]
      [1913 Webster]

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

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "caption":
   banner, banner head, drop head, dropline, epigraph, hanger, head,
   head up, heading, headline, jump head, legend, motto, overline,
   rubric, running head, running title, scarehead, screamer, spread,
   spreadhead, streamer, subhead, subheading, subtitle,
   superscription, title, title page, underline



Bouvier's Law Dictionary, Revised 6th Ed (1856):

CAPTION, practice. That part of a legal instrument, as a 'Commission,
indictment, &c., which shows where, when, and by what authority it was
taken, found or executed. As to the forms and requisites of captions, see 1
Murph. 281; 8 Yerg. 514; 4 Iredell, 113; 6 Miss,. 469; 1 Scam. 456; 5 How.
Mis. 20; 6 Blackf. 299; 1 Hawks, 354; 1 Brev. 169.
     2. In the English practice, when an inferior court in obedience to the
writ of certiorari, returns an indictment into the K. B., it is annexed to
the caption, then called a schedule, and the caption concludes with stating,
that "it is presented in manner and form as appears in a certain indictment
thereto annexed," and the caption and indictment are returned on separate
parchments. 1 Saund. 309, n. 2. Vide Dane's Ab. Index, h.t.
     3. Caption is another name for arrest. CAPTIVE. By this term is
understood  one who has been taken; it is usually applied to prisoners of
war. (q.v.) Although he has lost his liberty, a captive does not by his
captivity lose his civil rights.