Expand, amplify, swell, distend, inflate, dilate mean to increase or to cause to increase in size, bulk, or volume.
Expand is the most inclusive term in this group and may often be used interchangeably with any of the others. It distinctively implies enlargement by opening out, unfolding, or spreading and may be used when the enlarging force is either internal or external.
Amplify implies extension of something which is inadequate or obscure (as by filling out with details or by magnifying the volume).
Swell implies expansion beyond a thing’s original circumference or normal limits. Often it implies increase in intensity, force, or volume or it may imply puffing up or puffing out to the point of bursting.
Distend implies swelling caused by pressure from within forcing extension outward in all directions. It may presuppose a previous void or flaccid state or it may imply an exceeding of normal bounds.
Inflate usually implies distention by artificial means (as by the introduction of gas or by puffing up with something as insubstantial or as easily dissipated as gas).
Dilate implies expansion in diameter; it therefore suggests a widening out of something circular rather than a puffing up of something globular or spherical.