Definition of "on the hook"

For now, at least, Mr. Wedell, who is a vice president at the Robinson-Humphrey Company, a subsidiary of Shearson Lehman, is still on the hook for unsettled claims.

1991 October 27, Barbara Presley Noble, “Making a Difference: Lloyd's 'Indentured Servant'”, in New York Times, retrieved 15 June 2011

Yes, incumbents of both parties—especially those incumbents facing tough re-election campaigns—don't want to be on the hook for this vote.

2008 September 29, “Washington to Wall Street: Drop Dead”, in Newsweek, retrieved 15 June 2011

Could taxpayers really be on the hook for UAW pensions? Yes.

2010 April 15, Joseph R. Szczesny, “GM's Pension: A Ticking Time Bomb for Taxpayers?”, in Time