The word "undebased" means pure or untarnished. Therefore, the antonyms for "most undebased" would be words that describe something that is corrupted or impure. Some possible options could include words like contaminated, degraded, polluted, tainted, or spoiled. These words suggest that something once pure has been sullied or ruined, perhaps by outside influences or negative circumstances. Conversely, the concept of "most undebased" suggests something that is still very clear and true, without compromise or flaw. This could be applied to people, objects, or ideas that remain unblemished despite external pressures or challenges.