Laws are a dead letter, without courts to expound and define their true meaning and operation.

Playing-cards — the devil's picture-books — were hated by the Puritans like the very devil; […] The fine for selling these cards must have been a dead letter, for we find in the newspapers proof of the prevalence of card-playing.

1905, Basil Hall Chamberlain, Things Japanese, Railways
The most formidable obstacle in the way of Japanese railway enterprise is that conflicting interests and local intrigues are apt to render the law of expropriation for public benefit little more than a dead letter.

But since, in all these states, the grand juries and the courts refuse to act, the laws are dead letters.

I have thought proper to premise thus much, lest the incredible tale I have to tell should be considered rather the raving of a crude imagination, than the positive experience of a mind to which the reveries of fancy have been a dead letter and a nullity.

Dead letter

Meaning

Noun