WordNet sense 1 (an official document granting a right or privilege):

letters patent

WordNet sense 2 (a document granting an inventor sole rights to an invention):

patent of invention

WordNet sense 3 (free from impediment or obstruction or hindrance):

unobstructed

WordNet sense 4 (clearly revealed to the mind or the senses or judgment):

apparent, evident, manifest, plain, unmistakable

WordNet sense 5 (easily perceived by the senses or grasped by the mind):

obvious