Autarky is more than a ten-dollar word for self-sufficiency, as it implies a number of questions that “self-sufficiency” alone might not.
The ability to survive without trade or aid from other nations, for example, is not the same as the ability to reap enormous profits or grow one’s economy without trade with other nations. In other words, 'self-sufficiency' in terms of survival does not necessarily imply prosperity, but it does imply freedom of action without dependency on foreign approval, capital, resources, and expertise.