The Collaborative International Dictionary of English v.0.48:

Sanctification \Sanc`ti*fi*ca"tion\, n. [L. sanctificatio: cf.
   F. sanctification.]
   1. The act of sanctifying or making holy; the state of being
      sanctified or made holy; esp. (Theol.), the act of God's
      grace by which the affections of men are purified, or
      alienated from sin and the world, and exalted to a supreme
      love to God; also, the state of being thus purified or
      sanctified.
      [1913 Webster]

            God hath from the beginning chosen you to salvation
            through sanctification of the Spirit and belief of
            the truth.                            --2 Thess. ii.
                                                  13.
      [1913 Webster]

   2. The act of consecrating, or of setting apart for a sacred
      purpose; consecration. --Bp. Burnet.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sanctification
    n 1: a religious ceremony in which something is made holy

Easton's 1897 Bible Dictionary:

Sanctification
   involves more than a mere moral reformation of character,
   brought about by the power of the truth: it is the work of the
   Holy Spirit bringing the whole nature more and more under the
   influences of the new gracious principles implanted in the soul
   in regeneration. In other words, sanctification is the carrying
   on to perfection the work begun in regeneration, and it extends
   to the whole man (Rom. 6:13; 2 Cor. 4:6; Col. 3:10; 1 John 4:7;
   1 Cor. 6:19). It is the special office of the Holy Spirit in the
   plan of redemption to carry on this work (1 Cor. 6:11; 2 Thess.
   2:13). Faith is instrumental in securing sanctification,
   inasmuch as it (1) secures union to Christ (Gal. 2:20), and (2)
   brings the believer into living contact with the truth, whereby
   he is led to yield obedience "to the commands, trembling at the
   threatenings, and embracing the promises of God for this life
   and that which is to come."

     Perfect sanctification is not attainable in this life (1 Kings
   8:46; Prov. 20:9; Eccl. 7:20; James 3:2; 1 John 1:8). See Paul's
   account of himself in Rom. 7:14-25; Phil. 3:12-14; and 1 Tim.
   1:15; also the confessions of David (Ps. 19:12, 13; 51), of
   Moses (90:8), of Job (42:5, 6), and of Daniel (9:3-20). "The
   more holy a man is, the more humble, self-renouncing,
   self-abhorring, and the more sensitive to every sin he becomes,
   and the more closely he clings to Christ. The moral
   imperfections which cling to him he feels to be sins, which he
   laments and strives to overcome. Believers find that their life
   is a constant warfare, and they need to take the kingdom of
   heaven by storm, and watch while they pray. They are always
   subject to the constant chastisement of their Father's loving
   hand, which can only be designed to correct their imperfections
   and to confirm their graces. And it has been notoriously the
   fact that the best Christians have been those who have been the
   least prone to claim the attainment of perfection for
   themselves.", Hodge's Outlines.