to meddle, especially for the purpose of altering, damaging, or misusing (usually followed by with): Someone has been tampering with the lock.
2.
to make changes in something, especially in order to falsify (usually followed by with): to tamper with official records.
3.
to engage secretly or improperly in something.
4.
to engage in underhand or corrupt dealings, especially in order to influence improperly (usually followed by with): Any lawyer who tries to tamper with a jury should be disbarred.
1567, figurative use of tamper "to work in clay, etc., so as to mix it thoroughly," probably originally a variant of temper (q.v.), which is how it was initially spelled. Perhaps it is a dialectal workmen's pronunciation. Tamperproof is recorded from 1886.