1. To expose something to or contaminate something with some substance or agent that is infectious, toxic, or otherwise dangerous or unpleasant. He has been arrested for tainting the water supply with a nerve agent. They have been forced to recall nearly 3 million tons of canned tomatoes that may have been tainted with botulin.

2. To spoil, ruin, or degrade something positive with the presence or introduction of something terrible, tragic, or deeply unpleasant. Often used in passive constructions. You may have won, but your victory is tainted with blood of thousands of innocent people. He is tainting an otherwise incredible career with this scandalous behavior.