A person or thing that contaminates; something that introduces unwanted substances or makes something unclean.
From contaminate + -or/-er (suffix forming agent nouns, from Latin -or, meaning one who does the action). The pattern is: verb → agent noun, so contaminate becomes contaminator.
In crime scenes, investigators look for the 'contaminator'—the person whose DNA or evidence they find—but every investigator walking through the scene also becomes a contaminator, which is why crime labs are so obsessively careful.
Complete word intelligence in one call. Free tier — 50 lookups/day.