These words agree in meaning to become or cause to become larger. Swell is the most general of these terms, and means to increase in bulk or dimension in any way, as by adding air or by absorbing moisture: a mosquito bite that swelled to the size of a pea; a creek swollen into a river. Inflate , on the other hand, means specifically to expand by filling with gas or air: to inflate a balloon or a tyre. Both swell and inflate are commonly used in extended senses; swell can apply to any large increase ?inflate always, and swell sometimes, applying to disproportionately large or exaggerated increases: a small business that swelled into a big company almost overnight; to swell the funds of the charitable organization to a record amount; an inflated sense of his own importance. Swell has in many contexts a suggestion of morbidity or unnatural size, illustrated by its metaphorical use in the popular expression "a swelled head," meaning an inflated self-esteem.

Bulge implies swelling outwards, usually in one particular direction.

• Inferior tubes will bulge at their weakest spots; a small boy’s pocket bulging with marbles.

Distend means to expand or stretch out because of pressure exerted from within.

• When you take a deep breath and hold it, your lungs are distended ; A nursing mother’s breasts are distended with milk.

Whereas distend implies an enlargement in all directions, dilate usually implies a two-dimensional enlargement, and is most often applied to the eyes: eyes dilated with surprise; Pupils dilate when one moves from a sunny to a darkened room.