WordNet sense 1 (corrupt morally or by intemperance or sensuality):

corrupt, debauch, demoralize, deprave, misdirect, pervert, profane, subvert, vitiate, demoralise, pervert

WordNet sense 2 (lower in value by increasing the base-metal content):

alloy, alloy

WordNet sense 3 (corrupt, debase, or make impure by adding a foreign or inferior substance; often by replacing valuable ingredients with inferior ones):

adulterate, dilute, stretch, adulterate