Stepbrother

(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.

Thesaurus Entries

auntie, blood brother, brethren, brother, bub, bubba, bud, buddy, country cousin, cousin, cousin once removed, cousin twice removed, daughter, father, first cousin, foster brother, frater, grandnephew, grandniece, granduncle, great-aunt, great-uncle, half brother, kid brother, mother, nephew, niece, nuncle, nunks, nunky, second cousin, sis, sissy, sister, sister-german, sistern, son, stepbrother, stepsister, unc, uncle, uncs, uterine brother