Source : Webster's Revised Unabridged Dictionary (1913)

Sincere \Sin*cere"\, a. [Compar. {Sincerer}; superl.
   {Sincerest}.] [L. sincerus, of uncertain origin; the first
   part perhaps akin to sin- in singuli (see {Single}), and the
   second to cernere to separate (cf. {Discern}): cf. F.
   sinc[`e]re.]
   1. Pure; unmixed; unadulterated.

            There is no sincere acid in any animal juice.
                                                  --Arbuthnot.

            A joy which never was sincere till now. --Dryden.

   2. Whole; perfect; unhurt; uninjured. [Obs.]

            The inviolable body stood sincere.    --Dryden.

   3. Being in reality what it appears to be; having a character
      which corresponds with the appearance; not falsely
      assumed; genuine; true; real; as, a sincere desire for
      knowledge; a sincere contempt for meanness.

            A sincere intention of pleasing God in all our
            actions.                              --Law.

   4. Honest; free from hypocrisy or dissimulation; as, a
      sincere friend; a sincere person.

            The more sincere you are, the better it will fare
            with you at the great day of account. --Waterland.

   Syn: Honest; unfeigned; unvarnished; real; true; unaffected;
        inartificial; frank; upright. See {Hearty}.

Source : WordNet®

sincere
     adj 1: open and genuine; not deceitful; "he was a good man, decent
            and sincere"; "felt sincere regret that they were
            leaving"; "sincere friendship" [ant: {insincere}]
     2: characterized by a firm and humorless belief in the validity
        of your opinions; "both sides were deeply in earnest, even
        passionate"; "an entirely sincere and cruel tyrant"; "a
        film with a solemn social message" [syn: {earnest}, {in
        earnest(p)}, {solemn}]