Definition
A Latin legal term meaning "dangerous" or "perilous," derived from *periculum* (danger). In legal usage, *periculosus* appears principally as a qualifier in maxims and learned commentary to signal that a course of action — typically the introduction of novel legal doctrine or unprecedented practice — carries inherent risk of harm or disorder. The term does not name a cause of action, status, or remedy; it functions as jurisprudential caution language embedded in Latin maxims.
The most frequently encountered form is the maxim: *Periculosum est res novas et inusitatas inducere* — "It is dangerous (or perilous) to introduce new and untried things." This maxim, cited by Coke, expresses the common law's structural conservatism: that judicial innovation, however well-intentioned, carries risks that settled precedent avoids.
Common Language
Modern common usage (Wiktionary): No standard English entry. The root "perilous" means involving serious danger or risk.
Historical common usage (Webster's 1913): "Perilous" — full of, attended with, or involving peril; dangerous; hazardous.
The common English meaning of "perilous" maps closely to *periculosus*, but the legal significance is narrower: in classical and early modern legal Latin, the term operates not as a descriptive adjective about physical danger but as a doctrinal signal about the risks of jurisprudential departure from established norms. The danger in question is institutional, not physical.
Why It Matters in Research
Researchers encountering *periculosus* in historical legal sources will find it almost exclusively embedded in maxims rather than operative legal rules. This distinguishes it from terms that carry doctrinal weight on their own. The critical maxim — *Periculosum est res novas et inusitatas inducere* — appears in Coke on Littleton and surfaces in early American judicial opinions and treatises as shorthand for resistance to novel legal arguments. A researcher tracing the common law's attitude toward precedent and legal change will encounter this term as evidence of that conservatism.
Two research traps are worth flagging. First, the term appears in fragmentary form in Burrill's entry, which suggests the original source text was partially corrupted or truncated in transmission — the Ohio Reports citation embedded in Burrill's entry appears to be typographical noise from a nearby entry, not a citation to authority for *periculosus* itself. Researchers should not treat that Ohio citation as directly supporting the maxim. Second, because *periculosus* is Latin vocabulary rather than a technical term of art with a fixed doctrinal definition, its meaning in any given source depends on context. Verify the full maxim before citing; variant phrasings exist in the civil law tradition as well.
The companion maxim fragment preserved in Burrill — *Periculosum existimo quod bonorum virorum non* — translates roughly as "I consider dangerous what good men do not [approve]," a sentiment attributed in the civil law tradition to Neratius. This variant shifts the emphasis from novelty to moral consensus as a check on legal action. Both formulations reinforce the same underlying jurisprudential posture.
Historical Dictionary Support
Burrill's Law Dictionary is the primary historical source for this term in the Law Mind corpus. Burrill's entry is brief and confirms the definition (dangerous; perilous), provides the core maxim with a Coke citation, and preserves a fragment of a secondary maxim. The entry is notable for what surrounds it: the Ohio Reports reference embedded in the text is almost certainly a scanning or typesetting artifact from an adjacent entry, not a substantive citation. This is a known hazard with digitized historical law dictionaries and should alert corpus researchers to verify citations that appear anomalous in context.
No other historical dictionary in the Law Mind corpus provides a separate entry for *periculosus*. Black's Law Dictionary editions do not carry a standalone entry; the maxim appears instead under maxim collections. This means Burrill provides the most direct definitional authority available, and its brevity reflects the term's status as vocabulary rather than doctrine.
The Coke citation — Co. Litt. 379a — is genuine and well-established. Coke's commentary at that point in Littleton's Tenures addresses the risks of departing from settled legal understandings, making *periculosus* an authorial voice rather than a rule of decision.