A custom or usage that has acquired the force of law.

Roget 613: habit, habitude; assuetude^†, assuefaction^†, wont; run, way.    common state of things, general state of things, natural state of things, ordinary state of things, ordinary course of things, ordinary run of things; matter of course; beaten path, beaten track, beaten ground.    prescription, custom, use, usage, immemorial usage, practice; prevalence, observance; conventionalism, conventionality; mode, fashion, vogue; etiquette etc. (gentility) 852; order of the day, cry; conformity etc. 82; consuetude, dustoor^†.    one's old way, old school, veteris vestigia flammae [Lat.]; laudator temporis acti [Lat.].    rule, standing order, precedent, routine; red-tape, red-tapism^†; pipe clay; rut, groove.    cacoethes [Lat.]; bad habit, confirmed habit, inveterate habit, intrinsic habit &c.; addiction, trick.    training etc. (education) 537; seasoning, second nature, acclimatization; knack etc. ... meer laten zien