An intellectual is someone who can be given a topic and they will learn everything about it and then be able to generate original work based upon fundamental ideas. The cites on their work have a very long tail and it spills over into other fields. They are able to contribute across a wide domain. They open up new possibilities. They solve problems others cannot. They often and do bring down whole theories by looking at obscure things now seen as obvious.
An academic is someone who becomes very specialized in a very narrow topic based upon the fundamental work of others. The cites die out after a while and pertain to a very narrow field. They run into problems they cannot solve and they will ignore inconsistencies in favor of keeping their job. They are frequently intellectually timid.
Von Neumann was an intellectual as were Feynman and John Boyd to some degree.
