Most taintless means completely pure or without any blemish or contamination. The antonyms or opposite of this phrase could be terms such as tainted, stained, or impure. If something is considered tainted, it has been contaminated by some external or foreign substance or influence. Stained refers to something that has been soiled or marked in some way that cannot be remedied. Impure indicates that something is not in its natural or original state and has been mixed with other substances, leading to its degradation. Therefore, the opposite of most taintless is anything that detracts from its purity, including tainted, stained, and impure.