swelling vs oedema

swelling and oedema both are nouns.

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

As nouns, oedema is a hyponym of swelling; that is, oedema is a word with a more specific, narrower meaning than swelling:

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

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