The Collaborative International Dictionary of English v.0.48:

Retain \Re*tain"\, v. i.
   1. To belong; to pertain. [Obs.]
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            A somewhat languid relish, retaining to bitterness.
                                                  --Boyle.
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   2. To keep; to continue; to remain. [Obs.] --Donne.
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The Collaborative International Dictionary of English v.0.48:

Retain \Re*tain"\ (r[-e]*t[=a]n"), v. t. [imp. & p. p.
   Retained (r[-e]*t[=a]nd"); 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 restrain from departure, escape,
      or the like. "Thy shape invisible retain." --Shak.
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            Be obedient, and retain
            Unalterably firm his love entire.     --Milton.
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            An executor may retain a debt due to him from the
            testator.                             --Blackstone.
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   2. To keep in pay; to employ by a preliminary fee paid; to
      hire; to engage; as, to retain a counselor.
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            A Benedictine convent has now retained the most
            learned father of their order to write in its
            defense.                              --Addison.
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   3. To restrain; to prevent. [Obs.] --Sir W. Temple.
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   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.
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   Syn: To keep; hold; restrain. See Keep.
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WordNet (r) 3.0 (2006):

retain
    v 1: hold back within; "This soil retains water"; "I retain this
         drug for a long time"; "the dam retains the water"
    2: allow to remain in a place or position or maintain a property
       or feature; "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"; "She retained her composure"; "this garment
       retains its shape even after many washings" [syn: retain,
       continue, keep, keep on]
    3: secure and keep for possible future use or application; "The
       landlord retained the security deposit"; "I reserve the right
       to disagree" [syn: retain, hold, keep back, hold
       back]
    4: keep in one's mind; "I cannot retain so much information"