from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A brother to whom one is biologically related through one parent only.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A male sibling who has a different father, but the same mother. (Also known as maternal half brother)
- n. A male sibling who has a different mother, but the same father. (Also known as paternal half brother)
From Middle English half-brother, equivalent to half- + brother. Cognate with Dutch halfbroer ("halfbrother"), German Halbbruder ("halfbrother"), Danish halvbroder ("halfbrother"), Swedish halvbroder, halvbror ("halfbrother"), Icelandic hálfbróðir ("halfbrother"). (Wiktionary)