“Leave” is a noun in this case and indeed a synonym of “permission”. I suppose it can be confusing due to being a homonym to the verb “to leave” but it’s a rat

“Leave” is a noun in this case and indeed a synonym of “permission”. I suppose it can be confusing due to being a homonym to the verb “to leave” but it’s a rather common legal term (see AWOL, for instance). English, legal English in particular, is rife with apparent inconsistencies like this one. Because of its Anglo-Saxon roots and conquests by both the Danes and the Normans, who asserted their power in part through language, there are many concepts in English for which there are both words of Germanic and Latin, as well as French origin.