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tamper with someone or something
to fiddle with someone or something; to meddle with someone or something. I've got him believing just what I want him to believe. Don't tamper with him. Please don't tamper with the thermostat.
1. Interfere or meddle, especially in a harmful way. For example, If you tamper with that lock it's sure to break. [c. 1600]
2. Engage in improper or secret dealings, as in He was accused of tampering with the jury. [c. 1600]
To interfere with something in a harmful manner: Someone has been tampering with my mail—these letters have been opened! When jurors reported that they had been offered bribes, the judge told the defense not to tamper with the jury.