better half vs married person

better half and married person both are nouns.

Word	Noun	Adjective	Verb	Adverb
better half	Yes	No	No	No
married person	Yes	No	No	No

As nouns, better half and married person are synonyms defined as:

Other synonyms of better half include mate, partner, spouse.

better half (noun)	married person (noun)
a person's partner in marriage	a person's partner in marriage