Definition
En coste is a Law French phrase meaning "on the side" or "collateral." It describes a relationship that runs alongside or lateral to a main line rather than directly through it — most commonly used in discussions of collateral kinship, where a relative is connected through a common ancestor rather than by direct descent or ascent. A brother, for instance, stands en coste to his sibling: neither descends from the other, but both descend from a shared parent. The term situates a legal or genealogical relationship as lateral rather than lineal.
Common Confusion
En coste should not be conflated with collateral in the modern constitutional or financial sense. In property and succession law, collateral retains the same spatial metaphor — beside, not above or below — but modern usage has largely displaced the Law French form. Researchers encountering en coste in historical sources should read it as a descriptor of relationship geometry, not as a term of art with procedural or monetary content.
Why It Matters in Research
En coste appears almost exclusively in older English and American property and succession materials that draw on Law French terminology. Its practical relevance is narrow but specific: the term surfaces in treatises and abridgments discussing inheritance by collateral heirs, the canons of descent, and occasionally in fee tail analysis where the distinction between lineal and collateral succession determines who takes an estate.
Researchers working with pre-nineteenth-century property materials should be alert to the term appearing without gloss, on the assumption that the reader knows Law French. It will not appear in modern statutes or most twentieth-century case law. If you encounter it in a historical deed, pleading, or treatise passage, the interpretive move is straightforward: the relationship described is lateral, not lineal.
The term is also a navigational clue. Burrill cross-references it to COSTE, which is the parent entry. Researchers who find en coste in a source should consult the standalone entry for coste to understand the fuller doctrinal context in which the phrase was deployed — particularly in the rules governing which collateral relatives could inherit real property under the common law canons of descent.
No meaningful jurisdictional variation applies to this term because it is effectively obsolete as operative legal language. Its research significance is historical and interpretive rather than jurisdictional.
Historical Dictionary Support
Burrill's Law Dictionary provides the only entry captured here, rendering it briefly: "On the side; collateral. Kelham." The citation to Kelham refers to Robert Kelham's Dictionary of the Norman or Old French Language (1779), a standard reference for Law French terms. Burrill's entry is characteristically terse — consistent with his treatment of Law French phrases that function as descriptors rather than terms carrying independent doctrinal weight.
No substantive divergence exists across historical sources because the term's meaning is geometrically stable: it describes lateral placement in a genealogical or relational schema. What historical dictionaries do not do is explain why the distinction between lineal and collateral relationships mattered so intensely to the common law of real property — that doctrinal context must be recovered from treatises on descent and inheritance rather than from dictionary entries alone.