There seems to be no Geez lexicon available on Verbum. Dillmann's 19th-century lexicon is available online (Lexicon Linguae Aethiopicae) but that website does not always work, nor is there an option for offline use.
I guess that Leslau's concise lexicon would be much appreciated by anyone working with Geez. Leslau's comparative dictionary of Geez, by contrast, is less affordable and would not be purchased by as many people.