The Collaborative International Dictionary of English v.0.48:

Catchword \Catch"word`\, n.
   1. Among theatrical performers, the last word of the
      preceding speaker, which reminds one that he is to speak
      next; cue.
      [1913 Webster]

   2. (Print.) The first word of any page of a book after the
      first, inserted at the right hand bottom corner of the
      preceding page for the assistance of the reader. It is
      seldom used in modern printing.
      [1913 Webster]

   3. A word or phrase caught up and repeated for effect; as,
      the catchword of a political party, etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

catchword
    n 1: a favorite saying of a sect or political group [syn:
         motto, slogan, catchword, shibboleth]
    2: a word printed at the top of the page of a dictionary or
       other reference book to indicate the first or last item on
       that page [syn: guide word, guideword, catchword]

Moby Thesaurus II by Grady Ward, 1.0:

138 Moby Thesaurus words for "catchword":
   acknowledgments, adage, ana, analects, aphorism, apothegm, axiom,
   back, back matter, bastard title, battle cry, bibliography,
   bugle call, byword, call to arms, call-up, catch line,
   catch phrase, clarion, clarion call, cliche, clue,
   collected sayings, colophon, conscription, contents, contents page,
   copyright page, cry, cue, cue word, current saying, dedication,
   device, dictate, dictum, distich, endleaf, endpaper, endsheet,
   epigram, epigraph, epithet, errata, evidence, exhortation,
   expression, fad word, flyleaf, folio, fore edge, foreword,
   front matter, gnome, go for broke, golden saying, gung ho,
   half-title page, head, hint, hot lead, imprint, index, inscription,
   intimation, introduction, key, key word, lead, leaf, levy, makeup,
   maxim, mobilization, moral, mot, motto, muster, oracle, page,
   pet expression, phrase, pithy saying, precept, preface,
   preliminaries, prescript, proverb, proverbial saying, proverbs,
   rally, rallying cry, rebel yell, recruitment, recto, reverso,
   running title, saw, saying, scent, sentence,
   sententious expression, shibboleth, signature, slogan, sloka,
   spoor, stock saying, subtitle, suggestion, sutra,
   table of contents, tag line, tail, teaching, telltale, text,
   tip-off, title, title page, trace, trim size, trumpet call,
   type page, verse, verso, vestige, vogue word, war cry, war whoop,
   watchword, whiff, wisdom, wisdom literature, wise saying,
   witticism, word, words of wisdom