three-quarter sibling

Noun

 * 1) A sibling with whom one shares about 37.5% of one's genes, as opposed to 25% for half-siblings and 50% for full siblings.
 * 2)  The offspring of a horse's sire/dam that is by/out of a sibling of its other parent.
 * 3)  The offspring of a horse's dam and a son of its sire.
 * 4)  The offspring of a horse's sire and a daughter of its dam.