The Collaborative International Dictionary of English v.0.48:

Sentiment \Sen"ti*ment\, n. [OE. sentement, OF. sentement, F.
   sentiment, fr. L. sentire to perceive by the senses and mind,
   to feel, to think. See Sentient, a.]
   1. A thought prompted by passion or feeling; a state of mind
      in view of some subject; feeling toward or respecting some
      person or thing; disposition prompting to action or
      expression.
      [1913 Webster]

            The word sentiment, agreeably to the use made of it
            by our best English writers, expresses, in my own
            opinion very happily, those complex determinations
            of the mind which result from the cooperation of our
            rational powers and of our moral feelings.
                                                  --Stewart.
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            Alike to council or the assembly came,
            With equal souls and sentiments the same. --Pope.
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   2. Hence, generally, a decision of the mind formed by
      deliberation or reasoning; thought; opinion; notion;
      judgment; as, to express one's sentiments on a subject.
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            Sentiments of philosophers about the perception of
            external objects.                     --Reid.
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            Sentiment, as here and elsewhere employed by Reid in
            the meaning of opinion (sententia), is not to be
            imitated.                             --Sir W.
                                                  Hamilton.
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   3. A sentence, or passage, considered as the expression of a
      thought; a maxim; a saying; a toast.
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   4. Sensibility; feeling; tender susceptibility.
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            Mr. Hume sometimes employs (after the manner of the
            French metaphysicians) sentiment as synonymous with
            feeling; a use of the word quite unprecedented in
            our tongue.                           --Stewart.
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            Less of sentiment than sense.         --Tennyson.
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   Syn: Thought; opinion; notion; sensibility; feeling.

   Usage: Sentiment, Opinion, Feeling. An opinion is an
          intellectual judgment in respect to any and every kind
          of truth. Feeling describes those affections of
          pleasure and pain which spring from the exercise of
          our sentient and emotional powers. Sentiment
          (particularly in the plural) lies between them,
          denoting settled opinions or principles in regard to
          subjects which interest the feelings strongly, and are
          presented more or less constantly in practical life.
          Hence, it is more appropriate to speak of our
          religious sentiments than opinions, unless we mean to
          exclude all reference to our feelings. The word
          sentiment, in the singular, leans ordinarily more to
          the side of feeling, and denotes a refined sensibility
          on subjects affecting the heart. "On questions of
          feeling, taste, observation, or report, we define our
          sentiments. On questions of science, argument, or
          metaphysical abstraction, we define our opinions. The
          sentiments of the heart. The opinions of the mind . .
          . There is more of instinct in sentiment, and more of
          definition in opinion. The admiration of a work of art
          which results from first impressions is classed with
          our sentiments; and, when we have accounted to
          ourselves for the approbation, it is classed with our
          opinions." --W. Taylor.
          [1913 Webster]

WordNet (r) 3.0 (2006):

sentiment
    n 1: tender, romantic, or nostalgic feeling or emotion
    2: a personal belief or judgment that is not founded on proof or
       certainty; "my opinion differs from yours"; "I am not of your
       persuasion"; "what are your thoughts on Haiti?" [syn:
       opinion, sentiment, persuasion, view, thought]

Moby Thesaurus II by Grady Ward, 1.0:

185 Moby Thesaurus words for "sentiment":
   Amor, Christian love, Eros, Platonic love, admiration, adoration,
   affect, affection, affections, affective faculty, affectivity,
   agape, apprehension, ardency, ardor, assumption, attachment,
   attitude, bathos, belief, bias, bleeding heart, bodily love,
   brotherly love, caritas, charity, climate of opinion, cloyingness,
   common belief, community sentiment, conceit, concept, conception,
   conclusion, conjugal love, consensus gentium, consideration,
   conviction, desire, devotion, disposition, emotion,
   emotional charge, emotional life, emotional shade, emotionalism,
   emotions, emotivity, estimate, estimation, ethos, experience, eye,
   faithful love, fancy, feeling, feeling tone, feelings, fervor,
   finer feelings, flame, fondness, foreboding, free love,
   free-lovism, general belief, goo, gut reaction, heart,
   hearts-and-flowers, heartthrob, hero worship, idea, idolatry,
   idolism, idolization, image, imago, impression, inclination,
   inclining, intellectual object, judgement, judgment,
   lasciviousness, leaning, libido, lights, like, liking, love,
   lovemaking, married love, maudlinness, mawkishness, memory-trace,
   mental attitude, mental image, mental impression, mind, mush,
   mushiness, mystique, namby-pamby, namby-pambyism, namby-pambyness,
   nostalgia, nostomania, notion, observation, opinion, outlook,
   oversentimentalism, oversentimentality, partiality, passion,
   passions, penchant, perception, personal judgment, persuasion,
   physical love, point of view, popular belief, popular regard,
   popularity, position, posture, predilection, predisposition,
   presentiment, presumption, prevailing belief, profound sense,
   propensity, psychology, public belief, public opinion, reaction,
   recept, reflection, regard, representation, response, romanticism,
   sensation, sense, sensibilities, sensibility, sentimentalism,
   sentimentality, sentiments, sex, sexual love, shine, sight, slop,
   sloppiness, slush, soap opera, sob story, spiritual love, stance,
   supposition, susceptibilities, susceptibility, sweetness and light,
   sympathies, tearjerker, tendency, tender feeling, tender passion,
   tender susceptibilities, tenderness, theory, thinking, thought,
   truelove, undercurrent, uxoriousness, view, way of thinking,
   weakness, worship, yearning