rubric

Rubric comes from Middle English rubriche or rubrike, from Old French rubrique, from Latin rūbrīca, meaning 'red ochre' — the substance used to make red letters. That in turn traces back to Latin ruber, 'red,' and ultimately to the Proto-Indo-European root *h₁rewdʰ-.

Because red ink was used to mark headings, instructions, or important sections in manuscripts, the word for the red substance itself came to stand for those set-apart headings and guidelines.

It shares its root, ruber ('red'), with other English words descended from the same Proto-Indo-European base for 'red,' though no specific cognate is given here.