a Provençal sauce made from pounded red chillies, garlic, breadcrumbs, and other ingredients blended with stock, typically added to bouillabaisse: [mass noun]:croutons and rouille on the side [count noun]:it’s a lusty affair served with a properly pungent rouille
Origin:
French, literally 'rust', with reference to the colour
rouille in other Oxford dictionaries
Definition of rouille in the US English dictionary