backdoor
From Longman Dictionary of Contemporary Englishbackdoorback‧door /ˈbækdɔː $ -dɔːr/ adjective [only before noun] PGSECRETsecret, or not publicly stated as your intention a backdoor tax riseExamples from the Corpusbackdoor• a backdoor diplomatic solution• It is a move that many see as backdoor nationalisation.• Paid $ 100 for it in a backdoor transaction.