The phrase "secret retainer" refers to someone who is paid to provide help or support to another person, but their role is kept private and not openly acknowledged or known by others. Full definition
«Politicians are supposed to be on the people's payroll, not on secret retainer to wealthy special interests they do favors for,» he continued. (observer.com)
Howe also received a second secret retainer on his own through an LLC he created, Potomac Strategies, that he concealed from his bosses at WOH. (timesunion.com)
In another, it said, «Bharara: Politicians are supposed to be on the ppl's payroll, not on secret retainer to wealthy special interests they do favors for.» (newyork.cbslocal.com)