half-sister vs stepsister

half-sister and stepsister both are nouns.

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

As nouns, half-sister and stepsister are synonyms defined as:

half-sister and stepsister: a sister who has only one parent in common with you

Other synonyms of half-sister include half sister.

half-sister (noun)	stepsister (noun)
a sister who has only one parent in common with you	a sister who has only one parent in common with you