expand, amplify, swell, distend, inflate, dilate mean to increase in size or volume.

expand may apply regardless of the manner of increase (such as growth, unfolding, addition of parts).

amplify implies the extension or enlargement of something inadequate.

swell implies gradual expansion beyond a thing's original or normal limits.

distend implies outward extension caused by pressure from within.

inflate implies expanding by introduction of air or something insubstantial and suggests a vulnerability to sudden collapse.

dilate applies especially to expansion of circumference.