Lexicography in the Arab world has had important effects on the development of the Arabic language. The origin and subsequent development and refinement of traditional Arabic grammatical theory—as early as the eighth century- had intimate links with the practice of writing dictionaries. The Kitab al-ʿayn, by al-Khalil ibn Ahmad (d.c.786), which is the first full-scale dictionary in the Arab world, marked a significant milestone in the history of grammatical thought and set the tone for more works on Arabic grammar. For many centuries, the general mode of the theory has acknowledged a "closed" corpus of Qur'anic diction and pre-Islamic poetry and prose as the major source of Arabic lexicographic works. The main credo is that Arabic dictionaries should contain the "unattained" forms of the language and remain impervious to external persuasions; namely colloquialisms, borrowings, neologisms, and coinages. Arabic dictionaries continued to resist the slightest reform as to the codification of lexical innovations and the treatment of lexical gaps exhausting themselves to the point of stagnation. Today, English-Arabic dictionary editors have to deal with a huge number of lexical gaps that have cumulated over time. The lexical gap-filling process is carried out in a very unsystematic way that is far from creating an atmosphere of cooperation that ultimately contributes to creating unified English-Arabic lexical databases for lexicographic purposes. The paper explains how a modern English-Arabic dictionary can fall short in its modernizing role, and gives a snapshot of the most salient microstructural issues that characterize the Al-Mawrid Al-Hadeeth: A Modern English-Arabic Dictionary (2010).