tamper (v.)
"meddle, interfere," 1560s, figurative use of tamper "to work in clay, etc., so as to mix it thoroughly," probably originally a variant of temper (v.), which is how it often was spelled at first. Perhaps it is a dialectal workmen's pronunciation. Related: Tampered; tampering.
tamper (n.)
"one who or that which tamps," 1864, agent noun from tamp (v.).