The Collaborative International Dictionary of English v.0.48:

meaningful \meaningful\ adj.
   Having a meaning or purpose; having significance; as, a
   meaningful explanation; a meaningful discussion; a meaningful
   pause; to live a meaningful life. Opposite of meaningless.
   [Narrower terms: comprehensible, understandable;
   indicative, significative, suggestive ; {meaty, substantive
   ; {purposeful] Also See: purposeful, significant,
   important.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

meaningful
    adj 1: having a meaning or purpose; "a meaningful explanation";
           "a meaningful discussion"; "a meaningful pause" [ant:
           meaningless, nonmeaningful]

Moby Thesaurus II by Grady Ward, 1.0:

101 Moby Thesaurus words for "meaningful":
   allegorical, associational, augural, big, connotational,
   connotative, consequential, considerable, deep, definable,
   demonstrative, denominative, denotational, denotative, designative,
   diagnostic, eloquent, emblematic, evidential, exhibitive,
   expressive, extended, extensional, facund, figural, figurative,
   forerunning, foreshadowing, foreshowing, foretokening, forewarning,
   full of meaning, full of point, full of substance, graphic,
   heavy with meaning, identifying, ideographic, idiosyncratic,
   imaginative, implicative, important, indicating, indicative,
   indicatory, individual, intelligible, intensional, interpretable,
   intuitive, material, meaning, meaty, metaphorical, momentous,
   monitory, naming, pathognomonic, peculiar, pithy, pointed,
   precursive, precursory, predictive, prefigurative, pregnant,
   preindicative, premonitory, presageful, presaging, prognostic,
   prognosticative, readable, referential, relevant, representative,
   rich, semantic, semiotic, sententious, serious, signalizing,
   significant, significative, signifying, sober, substantial,
   substantive, suggestive, symbolic, symbolistic, symbological,
   symptomatic, symptomatologic, telling, transferred, typical, valid,
   vivid, warning, weighty