tamper

Short definition from Wiktionary

Noun

1. 1
   A person or thing that tamps: A tool used to tamp something down, such as tobacco in a pipe.
2. 2
   A person or thing that tamps: A railway vehicle used to tamp down ballast.
3. 3
   A person or thing that tamps: An envelope of neutron-reflecting material in a nuclear weapon, used to delay the expansion of the reacting material and thus produce a longer-lasting and more energetic explosion.

Verb

1. 1
   To make unauthorized or improper alterations, sometimes causing deliberate damage; to meddle (with something).
2. 2
   To try to influence someone, usually in an illegal or devious way; to try to deal (with someone).
3. 3
   To meddle (with something) in order to corrupt or pervert it.
4. 4
   To involve oneself (in a plot, scheme, etc.).
5. 5
   To attempt to practise or administer something (especially medicine) without sufficient knowledge or qualifications.
6. 6
   To discuss future contracts with a player, against league rules.