Well you've found an عيب in the dictionary! Currently it uses a single dictionary, Hans Wehr, which doesn't contain that word (I've checked in my physical copy also).

In my backlog is adding additional dictionaries to fill in where Hans Wher is lacking, with next in line Lane's Lexicon. Hans Wehr is a good dictionary for students and contains approximately 90% of the words they will encounter in their first few years of studying. The issue I'm having at the moment is that both dictionaries are structured differently and it requires some manual work to unify their structures.

When searching a verb you can either search the root letters, or any other form even with affixes attached and the stemming algorithms should get the right root word.