Source : Webster's Revised Unabridged Dictionary (1913)

Betray \Be*tray"\ (b[-e]*tr[=a]"), v. t. [imp. & p. p.
   {Betrayed} (-tr[=a]d"); p. pr. & vb. n. {Betraying}.] [OE.
   betraien, bitraien; pref. be- + OF. tra["i]r to betray, F.
   trahir, fr. L. tradere. See {Traitor}.]
   1. To deliver into the hands of an enemy by treachery or
      fraud, in violation of trust; to give up treacherously or
      faithlessly; as, an officer betrayed the city.

            Jesus said unto them, The Son of man shall be
            betrayed into the hands of men.       --Matt. xvii.
                                                  22.

   2. To prove faithless or treacherous to, as to a trust or one
      who trusts; to be false to; to deceive; as, to betray a
      person or a cause.

            But when I rise, I shall find my legs betraying me.
                                                  --Johnson.

   3. To violate the confidence of, by disclosing a secret, or
      that which one is bound in honor not to make known.

            Willing to serve or betray any government for hire.
                                                  --Macaulay.

   4. To disclose or discover, as something which prudence would
      conceal; to reveal unintentionally.

            Be swift to hear, but cautious of your tongue, lest
            you betray your ignorance.            --T. Watts.

   5. To mislead; to expose to inconvenience not foreseen to
      lead into error or sin.

            Genius . . . often betrays itself into great errors.
                                                  --T. Watts.

   6. To lead astray, as a maiden; to seduce (as under promise
      of marriage) and then abandon.

   7. To show or to indicate; -- said of what is not obvious at
      first, or would otherwise be concealed.

            All the names in the country betray great antiquity.
                                                  --Bryant.

Source : WordNet®

betraying
     adj : revealing unintentionally; "a betraying blush spread over
           her face"