old man vs common wormwood

old man and common wormwood both are nouns.

Word	Noun	Adjective	Verb	Adverb
old man	Yes	No	No	No
common wormwood	Yes	No	No	No

As nouns, old man and common wormwood are synonyms defined as:

old man and common wormwood: aromatic herb of temperate Eurasia and North Africa having a bitter taste used in making the liqueur absinthe

Other synonyms of old man include absinthe, Artemisia absinthium, lad's love.

old man (noun)	common wormwood (noun)
an informal term for your father	aromatic herb of temperate Eurasia and North Africa having a bitter taste used in making the liqueur absinthe
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