Sui generis
Sui generis (; ) is a Latin phrase that means "of its (his, her, their) own kind; in a class by itself; unique."
Issue (genealogy)
"Issue" typically means a person's lineal descendants—all genetic descendants of a person, regardless of degree. Issue is a narrower category than heirs, which includes spouses, ancestors, and collaterals (siblings, cousins, aunts, and uncles). This meaning of issue arises most often in wills and trusts. A person who has no living lineal descendants is said to have died without issue.