Definition
Isis is the historical name for the upper portion of the River Thames in England, specifically the stretch running from the river's source in the Cotswolds to its confluence with the River Thame near Dorchester-on-Thames, Oxfordshire. Beyond this point, the combined watercourse is known as the Thames. The name appears in older English legal and geographic sources when identifying riparian rights, navigation disputes, fishing rights, or other matters tied to this portion of the waterway.
Burrill also records a secondary geographic usage: Isis as a name for the River Ouse, reflecting the term's broader historical application to certain English rivers, though this usage is far less common in legal sources.
The term carries no independent legal doctrine of its own. Its significance in legal materials is purely locational — identifying the specific body of water at issue in a given dispute or grant.
Common Language
Modern common usage (Wiktionary): The River Thames between its source and its confluence with the River Thame at Dorchester on Thames.
Historical common usage (Webster's 1913): The principal goddess worshipped by the Egyptians, regarded as the mother of Horus and sister-wife of Osiris; also a genus of coral.
The legal usage tracks the geographic meaning rather than the mythological one. A researcher encountering "Isis" in older English legal materials — particularly those touching on Oxford, Oxfordshire riparian rights, or Thames navigation — should read it as a place name designating the upper Thames, not as a reference to Egyptian mythology or any other modern usage of the term.
Common Confusion
Modern researchers should be alert to two confounding usages unrelated to the legal-geographic meaning. First, ISIS is now a widely recognized acronym for the Islamic State of Iraq and Syria, a militant organization that has generated substantial contemporary legal material — including terrorism financing statutes, sanctions designations, and international criminal law proceedings — entirely unrelated to the English river. Second, the name appears in classical and religious contexts. Neither usage has any connection to the riparian and geographic sense operative in historical English law. When searching historical corpora, particularly those predating the twentieth century, "Isis" almost always refers to the river.
Why It Matters in Research
Researchers working with historical English property records, navigation acts, fishing rights grants, or Oxford college documents will encounter "Isis" as a straightforward geographic identifier. The practical research task is recognizing that the Isis and the Thames are the same physical river, distinguished only by the portion being referenced. Rights, duties, and grants that attach to "the Isis" in a historical document are rights attaching to the upper Thames and should be traced through the legal history of Thames navigation and riparian law accordingly.
The secondary Burrill reference to the River Ouse is an outlier and likely reflects either a scribal confusion or a highly localized usage. Researchers should not assume "Isis" means the Ouse without corroborating evidence from context.
The Black's 2nd Edition supplemental entry attributed to this term in the source material appears to be a misattribution or scanning artifact — the text quoted ("est jus eundi, ambulandi hominis | non etiam jumentum agendi vel vehiculum") is the definition of iter (a right of way in Roman law), not a definition of Isis. Researchers should disregard it as a corruption of the source and consult iter entries directly for that doctrine.
Historical Dictionary Support
Burrill's entry is minimal but accurate: it identifies Isis as the River Isis and, secondarily, the River Ouse. Black's 2nd Edition supplemental material, as noted above, does not appear to contain a genuine entry for Isis — the text supplied is a garbled version of an iter definition and should not be treated as authoritative on this term. Neither dictionary provides doctrinal content, which is consistent with the term's nature as a geographic identifier rather than a legal concept.
Jurisdictional Note
The term is specific to English law and geography. It has no parallel usage in American, Scottish, or other common law jurisdictions. Researchers working outside English historical materials are unlikely to encounter it.