Antonyms for the phrase "most thorough-going" refer to a lack of attention to detail or thoroughness in one's work or approach. Some possible antonyms include superficial, cursory, incomplete, half-hearted, haphazard, slapdash, or careless. These words suggest a person who does not take the time to fully consider all aspects of a project or task, and instead rushes through it without giving it the attention it deserves. When looking for antonyms for "most thorough-going," it's important to consider the context in which the phrase is being used and to choose words that accurately convey the opposite meaning.