badly
His sprained ankle had swollen badly.

slightly | up
Her feet swelled up after the long walk to the top of the hill.

with
Her legs had swollen with the heat.

heavy | gentle, slight | 10-foot, 20-foot, etc. | Atlantic, ocean
bobbing up and down like a small boat in a heavy ocean swell

break, come/roll in, lift sb/sth, surge up
The Atlantic swell surged up under them.

in a/the ~
The trawler rolled wildly in the heavy swell.

on/with the ~
The boat rose and fell with the swell.

firm, gentle, soft, warm

~ of
the gentle swell of her breasts