sister vs half-sister

sister and half-sister both are nouns.

Word	Noun	Adjective	Verb	Adverb
sister	Yes	No	No	No
half-sister	Yes	No	No	No

As nouns, half-sister is a hyponym of sister; that is, half-sister is a word with a more specific, narrower meaning than sister:

Other hyponyms of sister include big sister, little sister, half sister, stepsister.

sister (noun)	half-sister (noun)
a female person who has the same parents as another person	a sister who has only one parent in common with you
a female person who is a fellow member of a sorority or labor union or other group