trust company

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A commercial bank or other corporation that manages trusts.

from The Century Dictionary.

• noun A financial corporation organized under State laws, general or special, or both, to exercise the functions of a trustee.
• noun Such a corporation with added financial and other functions, varying in character and extent with the statutes of the different States and with the individual charter of the corporation.

from the GNU version of the Collaborative International Dictionary of English.

• Any corporation formed for the purpose of acting as trustee. Such companies usually do more or less of a banking business.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an organization (usually with a commercial bank) that is engaged as a trustee or fiduciary or agent in handling trust funds or estates of custodial arrangements or stock transfers or related services