Lehçe-i Osmânî is considered the most important work of Ahmet Vefik Pasha. This work is regarded as the first example of our modern lexicography tradition. With its second edition, which was re-edited by its author, Lehçe-i Osmânî was constructed with a striking structure that divides the vocabulary of Ottoman Turkish into Arabic-Persian origin and nonArabic-Persian. The handling of Turkish words as a headword in Ottoman lexicography started with Ahmet Vefik Pasha's Lehçe-i Osmânî. This work, which is the first in this respect, has become one of the main reference sources for Turkish scientists since the date it was written. In addition to these valuable features, Lehçe-i Osmânî also has some defects. The most important of these is that some head words are left undefined (very likely forgotten). Recep Toparlı (2000), who transferred the Lehçe-i Osmânî to Latin letters with a new order, stated that he determined the definitions of some of these items and added them to his study. But he stated that he did not include some items that he could not identify in his study. This study was primarily prepared to reveal the words and undefined items for which the definitions could not be determined by Toparlı. Some of the undefined words were defined by help of in-dictionary, some others outside from dictionary. These additions were given by their sources and testimonies. The items, whose definition still cannot be found, were brought to the attention of researchers who may be interested in the subject in the future.