The term 'Diminishing Layer' refers to the OZONE layer, which is a layer of gas in the Earth's atmosphere that protects us from the sun's ultraviolet radiation. The crossword solution for this term is 'OZONE, ' which is a molecule made up of three oxygen atoms. The OZONE layer has been slowly diminishing due to human activities such as the release of chlorofluorocarbons (CFCs) into the atmosphere. This has caused an increase in the amount of UV radiation reaching the Earth's surface, leading to a variety of health and environmental problems.