half sibling

Short definition from Wiktionary

Noun

1. 1
   A sibling sharing a single parent, as distinguished from a full-sibling or sibling-german, from a stepsibling, or from a sibling-like figure such as a blood sibling.
2. 2
   Any of two or more horses having the same dam but different sires.
3. 3
   Alternative spelling of half sibling.