n. The son of one's stepfather or stepmother who is not the son of one's mother and is not the son of one's father.
n. The stepson of one's father or mother which is not one's half-brother.
the GNU version of the Collaborative International Dictionary of English
n. A brother by the marriage of one's father with the mother of another, or of one's mother with the father of another.
The Century Dictionary and Cyclopedia
n. One's stepfather's or stepmother's son by a former marriage.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. a brother who has only one parent in common with you
Word Usage
"We could talk about all sorts of things while driving around the Northeast with the family (one thing I have always liked and respected about my stepbrother is his fierce intelligence - simply put, he's smarter than I am)."