hydrops vs swelling

hydrops and swelling both are nouns.

Word	Noun	Adjective	Verb	Adverb
hydrops	Yes	No	No	No
swelling	Yes	No	No	No

As nouns, swelling is a hypernym of hydrops; that is, swelling is a word with a broader meaning than hydrops:

hydrops: swelling from excessive accumulation of watery fluid in cells, tissues, or serous cavities
swelling: an abnormal protuberance or localized enlargement

Other hypernyms of hydrops include lump, puffiness.

hydrops (noun)	swelling (noun)
swelling from excessive accumulation of watery fluid in cells, tissues, or serous cavities	the increase in volume of certain substances when they are heated (often accompanied by release of water)
	something that bulges out or is protuberant or projects from its surroundings
	an abnormal protuberance or localized enlargement