The Collaborative International Dictionary of English v.0.48:

holding company \holding company\ n. (Finance)
   A company that controls other independently incorporated
   companies by ownership of most or all of their stock, but
   does not directly control the daily operations of those
   companies.
   [PJC]

WordNet (r) 3.0 (2006):

holding company
    n 1: a company with controlling shares in other companies

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "holding company":
   Aktiengesellschaft, aktiebolag, body corporate, business,
   business establishment, cartel, chamber of commerce,
   closed-end investment company, combine, commercial enterprise,
   compagnie, company, concern, conglomerate,
   conglomerate corporation, consolidating company, consortium,
   copartnership, corporate body, corporation,
   diversified corporation, enterprise, firm, growth fund, house,
   industry, investment company, investment trust,
   joint-stock association, joint-stock company, load fund,
   mutual fund, no-load fund, operating company, partnership,
   plunderbund, pool, public utility, stock company, syndicate,
   trade association, trust, utility