The superlative form of base; the lowest in quality, value, character, or morality; the most contemptible or dishonorable.
From Old English 'bas' + superlative suffix '-est.' The form has existed since at least Middle English to describe the absolute worst in any category.
The most interesting thing about 'basest' is that philosophers still debate what deserves the label—is selfishness baser than cowardice? Is theft baser than betrayal? Language preserves these arguments.
Complete word intelligence in one call. Free tier — 50 lookups/day.