A Muslim religious nut. Basically, an Arab who is frustrated by the shitty living standards of his own country, and gets brainwashed by the equally shitty government into thinking it is the West's fault. Some actively resist the "invaders", and subsequently get shot, incinerated or blown up. All in the hopes of banging virgins in Heaven.
Al Qaeda did 9/11, killing 3,000 Americans. America & Co. then retaliated, resulting in more than 100,000 Arab deaths in Iraq alone. And still Islamists claim they are winning this war.
A term used to describe militant individuals and organisations who use - or rather misuse - Islam (religion of Muslims) to further their political aims. They principally rely on terrorism and fear to obtain what they want and are helped by many governments who use these militants to instil fear into their own populace in order to justify an unnecessary reduction in civil liberties and the wanton disregard of privacy.
Most neutrals agree that they do not represent Islam or Muslims in the least.
See also Zionism, Christian Fundamentalism
He is known to be a member of an Islamist organisation which has carried out several terrorist activities over the past decade.
So-and-so is a well-known Islamist who has advocated the murder of innocents.