11 letters · 13 points in Scrabble
verb corrupt, debase, or make impure by adding a foreign or inferior substance; often by replacing valuable ingredients with inferior ones
adjective mixed with impurities
originThe adjectival sense's relation to adultery is the common theme that corruption or pollution has occurred; more at adulterate. By surface analysis, adulterate + -ed.
Etymology from Wiktionary, CC BY-SA 3.0