Definition
In feudal law, infidelitas denotes infidelity or faithlessness to one's feudal oath — the deliberate breach of the solemn bond of loyalty owed by a vassal to a lord. The feudal relationship was constituted and sustained by oath; infidelitas named the violation of that foundational obligation. It was not merely moral failure but a legal wrong carrying concrete consequences, including forfeiture of the fief and severance of the feudal relationship.
Common Language
Modern common usage (Wiktionary): "Infidelity" in contemporary English primarily denotes unfaithfulness in a romantic or marital relationship; secondarily, a lack of religious faith or adherence.
Historical common usage (Webster's 1913): Webster's defines "infidelity" first as disbelief in religion, particularly in Christianity, and second as unfaithfulness or breach of trust, with marital unfaithfulness listed as a specific application.
The gap between common and legal meaning here is substantial. Modern readers encountering infidelitas in a historical legal source will almost certainly import the domestic or religious connotation. In feudal law the term carries neither: it names a specific legal breach within the lord-vassal framework, with property, status, and political consequences entirely distinct from anything the modern word "infidelity" suggests.
Common Confusion
Infidelitas is sometimes conflated with treason (proditio) or rebellion, but the concepts are distinct. Infidelitas operated at the level of the individual feudal bond — one vassal's breach of oath to one lord. Treason in the higher medieval sense concerned the king or sovereign directly. A vassal could commit infidelitas toward a mesne lord without necessarily committing treason against the crown, though egregious infidelitas toward the crown could shade into both. Researchers should not assume the two terms are interchangeable in feudal instruments or commentary.
Why It Matters in Research
Infidelitas is a term of medieval Latin feudal law, and its appearance in primary sources signals that a document is operating within the feudal framework of oath, tenure, and forfeiture — not modern contract or tort. Researchers working in early English legal history, Scottish feudal records, or Continental sources drawing on the same tradition will encounter the term in discussions of forfeiture proceedings, divestiture of tenure, and the conditions under which a lord could reclaim a fief.
The primary research trap is anachronism. Translating infidelitas as "infidelity" and importing contemporary meaning will distort the legal analysis entirely. The word must be read against the feudal oath structure: the oath created legal status, and infidelitas destroyed it.
The term also appears in secondary commentary on feudal law, particularly in Spelman's Glossarium Archaiologicum, which all three source dictionaries cite as authority. Spelman is the foundational reference for this term in the English tradition, and researchers who need depth beyond dictionary entries should consult that source directly. No significant independent development of the term occurs in Black's or Burrill beyond what Spelman provides.
Because infidelitas is a term of extinct positive law rather than a living doctrine, it will not appear in modern statutory or case law. Its research relevance is confined to historical legal analysis, legal history, and the interpretation of feudal instruments and chronicles.
Historical Dictionary Support
All three source dictionaries — Black's (1st Ed.), Black's (2nd Ed.), and Burrill's — are in complete agreement: infidelitas means "infidelity; faithlessness to one's feudal oath," and all three cite Spelman as sole authority. There is no divergence, no elaboration, and no independent development across the three sources. The Black's (2nd Ed.) entry contains an editorial anomaly — the infidelitas definition appears embedded within the entry for "inferential," almost certainly a typographical artifact of that edition's production — but the substantive content is identical to the others.
The dictionaries offer a reliable but thin account. They identify the term correctly within its feudal context but provide no discussion of the legal consequences of infidelitas, the procedural mechanisms by which it was adjudicated, or its relationship to forfeiture doctrine. Researchers seeking that depth must go to Spelman directly or to modern legal historians working on feudal tenure.
Jurisdictional Note
Infidelitas is a term of medieval feudal law common to England and the Continent. In England, feudal tenure was formally abolished by the Tenures Abolition Act 1660, rendering the term a matter of legal history rather than operative law. Scottish feudal tenure persisted longer and was only formally abolished by the Abolition of Feudal Tenure etc. (Scotland) Act 2000, meaning infidelitas may appear in Scottish legal records across a longer timespan than in English sources.