be under somebody’s thumb
From Longman Dictionary of Contemporary Englishbe under somebody’s thumbbe under somebody’s thumbOBEYto be so strongly influenced by someone that they control you completely He was still under his father’s thumb. → thumbExamples from the Corpusbe under somebody’s thumb• Meg's really got Darren under her thumb.• He was showing her that she was under his thumb.• Judges are under the thumb of the bureaucracy.