Dictionaries can be regarded as important sources, wide fields, and tremendous linguistic prosperities as they contain items that represent outstanding heritage. This heritage offers to us a linguistic wealth in the different fields of language. With the passage of time, the dictionaries developed and they acquired a variety of forms, and different branches, so its importance increased. This study deals with Asahah Dictionary of Al-Jauhari, one of the important Arabic linguists in the fourth century AH, as it includes many aspects such as linguistics, grammar, and morphology. This study focuses on Al-Jauharis views on Diminution. Diminution is not just a change or modification in the structures and the formulas of the word, but it has many different connotations as humiliating, the reduction of number, approximating of time and place, endearment, and glorification. The scholars interested in the study of meanings through its construction and they invented special rules for this phenomenon which Al-Jauhari referred to it in his dictionary. This study aims to show this aspect focusing on Al-Jauharis views and the views of other scholars in order to understand the issues of Diminution which would enrich the morphological study.