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