[Latin, from opinio juris sive necessitatis (whether the opinion of law is compulsory)]
An essential element of custom, one of the four sources of international law as outlined in the Statute of the International Court of Justice. Opinio juris requires that custom should be regarded as state practice amounting to a legal obligation, which distinguishes it from mere usage.
From: opinio juris in A Dictionary of Law »
Subjects: Law — International Law