regula
/ˈrɛɡjʊlə/noun
1A rule or set of rules; a norm.
- Frequently with reference to Latin texts..
2In Doric architecture: a short narrow fillet or band situated below the taenia and aligned with the triglyph, frequently having a row of guttae or drops on the underside.
Origin
Old English. From classical Latin rēgula rod for drawing straight lines or measuring, ruler, basic principle, rule, rod, bar, (in the Doric order) smooth stone band under the taenia below each triglyph, in post-classical Latin also rule of faith, creed, symbol (early 3rd cent. in Tertullian), canon, regulation or code of ecclesiastical discipline, written monastic rule from regere to make or lead straight + -ula.