Slush fund

He is said to have used his party’s slush fund to buy votes in the election.

7: CERN bestows slush fund on the LHC. Take all pennies from the CERN space.

To do this, [the Lord Mayor] has at his disposal a multibillion-pound slush fund for use in lobbying the UK government and governments around the world to bring in laws that are friendly to banks and multinational companies.

A slush fund is a sum of money that is set aside as a reserve. In accounting, a slush fund is a general ledger account of commingled funds that does not have a designated purpose. In more sinister cases, a slush fund may be used as a "black fund," which is unaccounted for and kept off the books.