They are, in my opinion, slightly different notions, although they are frequently used interchangeably. Encapsulation is a design philosophy that involves building items that are equivalent to familiar objects/processes to aid understanding, whereas abstraction is more of a design philosophy that involves making products that are analogous to familiar objects/processes to aid understanding. Encapsulation is simply one of several abstraction techniques available.
Consider the word "windows." They are simply graphical squares on the screen, not windows in the classic sense. However, thinking of them as windows is helpful. That's a euphemism.
Encapsulation occurs when the "windows API" hides the intricacies of how text or graphics are physically produced within the limits of a window.