stepbrother vs half-brother

stepbrother and half-brother both are nouns.

Word	Noun	Adjective	Verb	Adverb
stepbrother	Yes	No	No	No
half-brother	Yes	No	No	No

As nouns, stepbrother and half-brother are synonyms defined as:

stepbrother and half-brother: a brother who has only one parent in common with you

Other synonyms of stepbrother include half brother.

stepbrother (noun)	half-brother (noun)
a brother who has only one parent in common with you	a brother who has only one parent in common with you