Terms of an art should be explained from the art.

Explanation

(English-origin maxim.) Technical terms must be defined by reference to the art or discipline from which they arise, not by common parlance — a term of art carries its specialized meaning.

Where this applies

• A medical malpractice case hinges on the word "proximate" — the court must define it according to its medical and legal meaning, not how a layperson might use it in casual conversation.
• A construction contract uses the term "substantial completion," and the parties disagree on whether it's met — the term must be defined by construction-industry standards, not everyday English.
• A patent dispute turns on the phrase "coefficient of friction" — the court must interpret it as an engineer would, not guess at a common-sense meaning.