consuetudo pro lege servatur

Custom is held as law.

Notes

Where there are no specific laws, the matter should be decided by custom; established customs have the force of laws. Also consuetudo est altera lex (custom is another law) and consuetudo vincit communem legem (custom overrules the common law); see also: Consuetudinary.

Words

lego – appoint, choose, collect, pass through, read, select, to gather
consuetudo – custom, familiar acquaintance, habit, intimacy, usage