Definition
In law, a sister is a female who shares one or both parents with another person. Where both parents are shared, she is a sister of the whole blood; where only one parent is shared, she is a half-sister or sister of the half blood. The term appears most frequently in statutes of descent and distribution, intestacy proceedings, and testamentary construction, where precise identification of a decedent's relatives determines inheritance rights.
The legal significance of the term turns almost entirely on context: whether a half-sibling qualifies under a given instrument or statute as a "sister" is a recurring interpretive question, and courts have not resolved it uniformly.
Common Language
Modern common usage (Wiktionary): A daughter of the same parents as another person; a female sibling. Also used for a female member of a religious order, a senior nurse, or any woman regarded as a close associate.
Historical common usage (Webster's 1913): A female who has the same parents with another person, or one of them only — more precisely a half-sister in the latter case. Also applied to women closely allied through faith, society, or shared condition.
The common meaning and the legal meaning largely align at their core, but the law draws a sharper internal distinction than ordinary speech does. In everyday English, "sister" almost always means full sibling, and "half-sister" is a separate, explicitly modified term. In legal instruments — particularly older wills and statutes — the word "sister" unmodified may or may not encompass half-sisters, and that ambiguity has generated genuine litigation. The legal dictionary entry is not just a definition but a warning: do not assume the common understanding controls.
Common Confusion
The central confusion is whether "sister" in a will, deed, or statute includes a half-sister. Courts have generally held that "sister" in its primary sense refers to a sister of the whole blood, but this presumption can be displaced by context, surrounding instrument language, or extrinsic evidence of the testator's intent. Anderson's notes that where construing "sister" to mean "half-sister" would divert property away from lineal descendants to strangers, the burden of proving that intent falls on the party asserting the broader reading. Researchers should not treat this as a settled default in either direction without examining the governing jurisdiction's rules of construction and the instrument's internal language.
Why It Matters in Research
The practical research stakes for "sister" are almost entirely in probate, estate, and family law contexts. Several issues recur:
Half-blood versus whole-blood distinction. Many older statutes of descent explicitly preferred or excluded half-bloods. When reading pre-20th-century materials, researchers must check whether the applicable statute drew this line and how courts in that jurisdiction applied the term "sister" in its absence.
Testamentary construction. Wills that use "sister" without modification present an ongoing interpretive challenge. The presumption favoring whole-blood siblings is real but rebuttable, and the evidentiary burden for rebuttal has varied across courts and periods. Anderson's treatment is the most practically useful of the historical sources on this point.
Statutory terminology drift. Modern intestacy statutes in most U.S. jurisdictions treat half-bloods and whole-bloods equally or nearly so, but the underlying case law often developed against a backdrop where they were not equivalent. Reading older decisions requires awareness that the word "sister" carried a more exclusive default meaning.
Institutional uses in historical sources. Historical legal materials — particularly those touching ecclesiastical law, charitable trusts, or hospital administration — may use "sister" to mean a nun or a nursing sister. This usage is not a legal term of art in the Anglo-American common law sense, but it can appear in trust instruments, bequest language, and organizational governance documents. Researchers in those areas should flag the context before assuming the familial meaning.
Historical Dictionary Support
Black's Law Dictionary (both the first and second editions) gives identical definitions: a woman sharing the same father and mother with another, or having one parent only in common. The definition is precise but thin — it identifies the whole-blood/half-blood distinction without resolving how courts should treat the word when it appears unmodified.
Bouvier's Law Dictionary matches Black's on substance and adds a useful structural note: in the primary sense, she is called "sister" simply; in the secondary sense, "half-sister." The citation to 61 How. Pr. 48 grounds this in New York practice. Bouvier's framing makes explicit what Black's only implies — that the unmodified word has a default meaning that may be overcome.
Anderson's Dictionary of Law is the most practically oriented of the four. Its cross-reference to CONSANGUINITY signals that researchers should not treat "sister" in isolation but as part of a broader relational structure that governs succession. Its note on testamentary burden-shifting is a useful doctrinal point the other dictionaries omit entirely.
None of the historical sources address the institutional or honorific uses of "sister" (religious orders, nursing), which is an appropriate omission for legal dictionaries but a gap to keep in mind when working with source materials outside the succession context.
Jurisdictional Note
Modern U.S. intestacy statutes, following the Uniform Probate Code's lead, generally treat relatives of the half blood the same as relatives of the whole blood. Older state statutes and common law rules varied considerably, with some jurisdictions giving half-bloods a reduced share or excluding them altogether. English common law historically disfavored half-bloods in descent, a rule that influenced early American law and persisted in some states well into the 20th century. Historical research in succession law must account for the governing statute's date and the jurisdiction's half-blood rule.