old man vs dysphemism

old man and dysphemism both are nouns.

Word	Noun	Adjective	Verb	Adverb
old man	Yes	No	No	No
dysphemism	Yes	No	No	No

As nouns, dysphemism is a hypernym of old man; that is, dysphemism is a word with a broader meaning than old man:

old man: an informal term for your father
dysphemism: an offensive or disparaging expression that is substituted for an inoffensive one

Other hypernyms of old man include begetter, father, male parent.

old man (noun)	dysphemism (noun)
an informal term for your father	an offensive or disparaging expression that is substituted for an inoffensive one
a man who is very old
a familiar term of address for a man
(slang) boss
aromatic herb of temperate Eurasia and North Africa having a bitter taste used in making the liqueur absinthe