It is reckoned for the ancient Arab scholars their freedom from subjectivity, that was when they set scientific criteria that are used to judge when proving linguistic differences between synonyms. Among the most famous Arab scholars who took this path was Abu Hilal Al-Askari, in his claim, he relied on a set of etymological criteria to differentiate between Arabic words that share a common semantic space. This research seeks to reveal the contribution of etymology in clarifying linguistic differences, and stand on the fields of knowledge that benefit from that treatment; therefore, the research uses the descriptive method to answer the following questions: -Are the etymological criteria accurate in their results? - Are the etymological criteria comprehensive to accommodate all examples? - What are the problems that prevent the effectiveness of the etymological criteria when applied? The research has identified the strengths and weaknesses of Abu Hilal Al-Askari's etymological level criteria.