Definition
A relational term describing the degree of blood connection between siblings who share both the same father and the same mother. Two individuals are of the full blood with respect to each other when they are born of the same two parents. The term stands in contrast to half blood, which describes siblings who share only one common parent.
The concept arises primarily in inheritance law, where the degree of blood relationship between a decedent and potential heirs can determine priority of succession, share size, or eligibility to inherit at all. In some legal systems and historical statutory schemes, full-blood relatives were favored over half-blood relatives in intestate succession.
Common Language
Modern common usage (Wiktionary): "Full blood" in ordinary English often appears in the phrase "full-blooded," meaning pure or thoroughbred, applied to animals or used figuratively to mean vigorous or complete.
Historical common usage (Webster's 1913): Webster's uses "full blood" and "full-blooded" to mean having the blood of a pure race or breed, without mixture; thoroughbred.
The common meaning carries connotations of racial or ethnic purity and has been applied in both animal husbandry and, historically and problematically, to human populations. The legal meaning is narrower and more precise: it concerns only the question of whether two specific individuals share both parents, without regard to any notion of racial or ethnic purity. Researchers should be alert to the fact that historical legal sources — particularly those involving Native American tribal membership and inheritance under federal Indian law — sometimes used "full blood" in ways that blurred this line, importing racial classification into what should have been a purely genealogical inquiry.
Common Confusion
FULL BLOOD vs. WHOLE BLOOD: The terms are interchangeable in substance. Black's notes that "whole blood" is the more usual term in modern law, and most contemporary statutes and courts use "whole blood" rather than "full blood." Researchers searching historical sources may encounter "full blood" where modern sources would say "whole blood." Both terms mean the same thing: descent from the same two parents.
FULL BLOOD vs. HALF BLOOD: These are the core opposing terms in this area of law. Half blood denotes a sibling relationship through one common parent only — either the same father with different mothers, or the same mother with different fathers. The legal significance of this distinction has varied considerably across time and jurisdiction, particularly in intestate succession schemes.
Why It Matters in Research
The primary research significance of "full blood" is terminological: it is the older form of what modern statutes almost universally call "whole blood." If you are researching intestate succession rules in sources predating the mid-twentieth century, you will encounter "full blood" frequently where a modern statute would say "whole blood." Treat the two as equivalent unless context suggests otherwise.
The distinction between full (whole) blood and half blood matters most in intestate succession research. Many historical statutes — and some modern ones — disadvantaged half-blood relatives in inheritance, either excluding them entirely, reducing their share, or requiring that whole-blood relatives of the same degree be exhausted before half-blood relatives could inherit. The degree to which this discrimination persisted varies sharply by jurisdiction and era.
A second and distinct research context is federal Indian law, where "full blood" and "full-blood Indian" appeared in federal statutes, treaties, and administrative determinations governing tribal membership, land allotments, and competency to manage property. In this context the term carried legal consequences tied to blood quantum calculations and was entangled with racial classification in ways that have been extensively criticized. Researchers working in this area should be aware that "full blood" in federal Indian law sources is not simply a kinship term but a legally constructed racial-genealogical category with its own distinct and troubled history.
A third context is conflict of laws in succession matters: when a decedent's estate involves property in multiple jurisdictions, or when heirs are connected to different legal systems (including tribal law), the applicable definition of full blood or the legal weight given to it may differ across those systems.
Historical Dictionary Support
Black's and Bouvier's are in complete agreement on the core meaning: full blood means descent from the same father and mother, denoting the strongest degree of sibling blood connection. Black's adds the Roman law reference — Justinian's Novels distinguish siblings "ex utroque parente conjuncti" (connected through both parents) from those sharing only one — grounding the concept in civil law as well as common law tradition. This is a useful reminder that the distinction between full and half blood is ancient and not merely a common-law artifact.
Black's editorial note that "whole blood" is the more usual modern term is the most practically important observation in either entry, and neither source explores the full-blood/half-blood distinction's consequences in intestate succession at any depth. Neither source addresses the federal Indian law usage at all, which is a significant gap for any researcher working in that area.
Jurisdictional Note
Virtually all U.S. jurisdictions now use "whole blood" in their intestate succession statutes, and the Uniform Probate Code has substantially reduced or eliminated the legal disadvantage historically placed on half-blood relatives. Some states retain provisions distinguishing whole-blood and half-blood heirs in specific circumstances. Federal Indian law materials use their own distinct framework for blood quantum that operates independently of state succession law.