Source : Webster's Revised Unabridged Dictionary (1913)

Retain \Re*tain"\, v. t. [imp. & p. p. {Retained}; p. pr. & vb.
   n. {Retaining}.] [F. retainir, L. retinere; pref. re- re- +
   tenere to hold, keep. See {Tenable}, and cf. {Rein} of a
   bridle, {Retention}, {Retinue}.]
   1. To continue to hold; to keep in possession; not to lose,
      part with, or dismiss; to retrain from departure, escape,
      or the like. ``Thy shape invisibleretain.'' --Shak.

            Be obedient, and retain Unalterably firm his love
            entire.                               --Milton.

            An executor may retain a debt due to him from the
            testator.                             --Blackstone.

   2. To keep in pay; to employ by a preliminary fee paid; to
      hire; to engage; as, to retain a counselor.

            A Benedictine convent has now retained the most
            learned father of their order to write in its
            defense.                              --Addison.

   3. To restrain; to prevent. [Obs.] --Sir W. Temple.

   {Retaining wall} (Arch. & Engin.), a wall built to keep any
      movable backing, or a bank of sand or earth, in its place;
      -- called also {retain wall}.

   Syn: To keep; hold; retrain. See {Keep}.

Retain \Re*tain"\, v. i.
   1. To belong; to pertain. [Obs.]

            A somewhat languid relish, retaining to bitterness.
                                                  --Boyle.

   2. To keep; to continue; to remain. [Obs.] --Donne.

Source : WordNet®

retain
     v 1: hold within; "This soil retains water"; "I retain this drug
          for a long time"
     2: allow to remain in a place or position; "We cannot continue
        several servants any longer"; "She retains a lawyer"; "The
        family's fortune waned and they could not keep their
        household staff"; "Our grant has run out and we cannot
        keep you on"; "We kept the work going as long as we could"
        [syn: {continue}, {keep}, {keep on}, {keep going}]
     3: secure and keep for possible future use or application; "The
        landlord retained the security deposit"; "I reserve the
        right to disagree" [syn: {hold}, {keep back}, {hold back}]
     4: keep in one's mind; "I cannot retain so much information"