Dormant commerce clause

The implied constitutional principle that prevents states from discriminating against or unduly burdening interstate commerce, even when Congress has not acted. It derives from the negative implication of Congress's power to regulate commerce among the states.

From Latin 'dormire' (to sleep) combined with 'commerce' from Latin 'commercium' (trade). The term emerged in 20th-century constitutional law to describe the 'sleeping' or inactive aspect of the Commerce Clause that still restricts state power even when Congress hasn't legislated.