melancholy vs body fluid

melancholy and body fluid both are nouns.

Word	Noun	Adjective	Verb	Adverb
melancholy	Yes	Yes	No	No
body fluid	Yes	No	No	No

As nouns, body fluid is a hypernym of melancholy; that is, body fluid is a word with a broader meaning than melancholy:

melancholy: a humor that was once believed to be secreted by the kidneys or spleen and to cause sadness and melancholy
body fluid: the liquid parts of the body

Other hypernyms of melancholy include bodily fluid, humor, humour, liquid body substance.

melancholy (noun)	body fluid (noun)
a humor that was once believed to be secreted by the kidneys or spleen and to cause sadness and melancholy	the liquid parts of the body
a feeling of thoughtful sadness
a constitutional tendency to be gloomy and depressed

melancholy (adjective)	body fluid (adjective)
grave or even gloomy in character
characterized by or causing or expressing sadness