The Collaborative International Dictionary of English v.0.48:

Earnestness \Ear"nest*ness\, n.
   The state or quality of being earnest; intentness; anxiety.
   [1913 Webster]

         An honest earnestness in the young man's manner. --W.
                                                  Irving.
   [1913 Webster]

WordNet (r) 3.0 (2006):

earnestness
    n 1: an earnest and sincere feeling [syn: earnestness,
         seriousness, sincerity]
    2: the trait of being serious; "a lack of solemnity is not
       necessarily a lack of seriousness"- Robert Rice [syn:
       seriousness, earnestness, serious-mindedness,
       sincerity] [ant: frivolity, frivolousness]

Moby Thesaurus II by Grady Ward, 1.0:

106 Moby Thesaurus words for "earnestness":
   abandon, absorption, advertence, advertency, alertness, ardency,
   ardor, assiduity, assiduousness, attention, attention span,
   attentiveness, awareness, care, commitment, committedness,
   concentration, consciousness, consideration, decidedness, decision,
   decisiveness, decorousness, dedication, definiteness, deliberation,
   demureness, determinateness, determination, determinedness,
   devotedness, devotion, devoutness, diligence, doggedness, ear,
   earnest, engrossment, faith, faithfulness, fervency, fervidness,
   fervor, fidelity, fire, firmness, formality, gravity, grimness,
   heartiness, heat, heatedness, heed, heedfulness, impassionedness,
   intensity, intentiveness, intentness, long face, loyalty,
   mindfulness, note, notice, observance, observation, obstinacy,
   passion, passionateness, perseverance, persistence, purpose,
   purposefulness, regard, regardfulness, relentlessness, remark,
   resoluteness, resolution, resolve, resolvedness, respect,
   sedateness, self-will, seriousness, sincerity, single-mindedness,
   sober-mindedness, soberness, sobersidedness, sobersides, sobriety,
   solemnity, solemnness, somberness, spirit, staidness,
   straight face, tenacity, thought, thoughtfulness, total commitment,
   vehemence, warmth, weightiness, will, zeal