noun ·Rare ·Advanced level

Definitions

Noun

1. 1
   The discredited theory that the speed of light has decreased over time, proposed by creationists in order to support the belief that the universe is a few thousand years old even though there are objects visible today that are billions of light years away (whereas a constant speed of light would indicate that the universe is billions of years old and so contradict this belief). uncountable

Etymology

From c (“the symbol used in physics for the speed of light”) + decay.

Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.