Looking at it historically--it's a fairly recent concept--I think "intellectual" varies with culture--though as I enumerated the following, it seemed that the common thread was "the claim to authority and privilege without the burden of power."
In the US, intellectual=egghead. Somebody who bothers about something that people with common sense would not.
In Russia/Eastern Europe before communism, an intellectual was a man who had the moral right to sit at the landowner's table without being rich or owning land himself. (At least, according to Dostoevsky)
In Russia/Eastern Europe after communism, an intellectual was a man who felt he had the right to write/think/control cultural values in complete isolation from the working class and without having to dirty his hands with power.
In Western europe, an intellectual is someone who claims the privileges of the upper class without dirtying his hands either with power or physical labor.
Joanna Bujes